Hello, it's nice to have another perspective on the matter especially from someone who is Latina, like Mari. But I completely understand what you mean. Now, give me some grace as it has been a minute since I've seen s1 and s2, so some things about Mari's character that I remember mostly revolve around s3. From what I can remember though, she did have moments of great bravery such as going with Akilah to help Nat find Lottie during a snow storm, as well as willingly agreeing to being a decoy so the others could get help, but also that she could scared at times (not only with her screaming in fear during s1, but also seeking comfort in mainly Akilah rather than really anyone else). Due to her being a secondary character who mostly consisted to the background, she didn't have much plot to pull from. But then s3, which was leaning towards making her more crucial to the plot, added more to that. Though, not by much as it seems more so focused on making her this not all there, lacking street smarts kind of girl but for insult purposes or comedic relief. And, while that within itself isn't so bad, it's not great with the fact that Mari is one of the poc characters who isn't given much depth in comparison to her yte counterparts. Paired along with a writer's room that often puts poc in harms way....not very great.
The show even had an opportunity to tie into her standoffish and bratty "mean" girl persona with the mention of her baby cousin. Having to be the only person there while a baby dies is traumatic, but even more so when it's your own family. This trauma could've made Mari develope an outer shell (she's easily snappy, resorting to mean and bratty retorts when unnecessary, seeing any flaws or weaknesses and airing them out, not wanting to tend to those who are sick, I could go on). Her being reluctant to help tend to Lottie and breaking down after could've been a result of her untouched grief. Her instantly clicking with Akilah could've been because she saw the same innocence from her cousin in her. When Shauna was giving birth, that could've been a perfect opportunity for her to grapple with what the loss reminded her of (just hiding it behind "Wilderness, please don't let Shauna die!")
And bringing it back to Mari's intelligence, the way she gravitated toward people in power or with high status so easily should have been noted better. Her connection with Jackie could have been just them being friends, so it would be a given that she rallies behind her. But for Nat and Lottie, this isn't the case or more so in the beginning. Mari makes snippy comments about Lottie and her visions, seeming to hold little interest in her besides deeming her as crazy. But once they're stuck in the cabin for the winter and Lottie becomes prophet like, Mari changes her tune. Could this be because she's afraid and needs something to cling too? Sure, but also it follows the pattern of her and people with status. She's very defensive and protective over Lottie, almost similar to how someone is regarding a religious figures and this impacts their relationship. There's layers too it. However, once Nat becomes queen and others begin to grow dismissive over Lottie and flock to their new leader, Mari follows suit and goes back to throwing insults at Lottie and viewing her as crazy. From what we've seen, Mari an Nat haven't really been that close to one another prior to s3, which shows them being allies. And while this could do with them trying to find rescue and oppose Shauna, Mari taking the time to have a heart to heart with Nat was a surprise. She's often more willingly to show a softer side of herself with those in power than others (with the exception of Akilah and, surprisingly, Gen who regards her [Mari] as her friend).
This could even tie into her protective and defensive nature as well, specifically towards people she cares about. With her easily flocking to people in power, there's a contrast to how she views and treats Shauan. For better or worse, mostly worse, she sews Shauna for who she is and doesn't back down but rather challenges her (to her downfall). There are many instances from the plot that could explain why Mari doesn't vibe with Shauna, from her hurting and indirectly being the reason Jackie dies, to her brutally beating Lottie, to being antagonistic to Nat, to her (as a result of making them have to stay another winter) making Akilah want to die---all of these people are close to Mari and have been harmed, directly and indirectly, by Shauna. So it would make sense that she wouldn't like her nor support her in any way. This also would've made her last words even more impactful, as she really gets the last laugh of karma with Shauna's life in the adult tl falling apart. Chef's kiss.
Season 3 had a lot of opportunities to build up on Mari's character, especially with what they had from the previous two seasons. However, they decided to the fumble the ball over an interesting woc and give more value (and some of her possible plot points) to a random yte girl who said one funny line and that was it, but held no importance further down the line of the plot after. This is a consistent theme with the Yellowjackets writers, who have made many of their woc actresses have to literally beg for more screentime and development for their characters. That within itself isn't a good look, but the lack of racial sensitivity in their script as well shows that there weren't any poc in the writer's room either. Because if there were, I don't think so many, especially Taissa who is a main, would've had their stories pushed to the side or revolving around white characters (eg. Travis). If there was, an Indigenous mentally ill girl wouldn't be brutally beaten by a white girl to help fuel her development and have their relationship never be mentioned again besides her (Lottie) being viewed as an antagonist in Shauna's mind. If there were, then you wouldn't have, not only, most of the Latin characters all die on the show, but have a brown girl be dehumanized by a white girl who took every opportunity she could to be cruel to her and wear her hair as a trophy. If there were poc writers for Yellowjackets, a lot of these implications would've been realized and handled better. And it makes it worse because some in the fandom, largely Shauna fans (though not all) are being either obtuse or purposely dismissive over the complaints. Some saying it's just "payback" for Mari trying to take Jackie's jacket, even though 1.) What Shauna did to Mari is in no way comparable to taking a jacket to use during a blizzard and 2.) Before Mari even dies, Shauna makes her take off her jacket so the comparison was already made by that point. Others are even going as far as to say that Mari is white rather than poc, as a way to dismiss the racial implications and the "Shauna is racist" jokes. And it's so laughable because when you put Mari with the other actual white people on the show, she does not give off white girl vibes, she is definitely a brown girl, like they are lying so hard to justify what Shauna did to her. It's so disgusting.
Sorry if this is all over the place and rather long, my rant would've been better formatted but I'm in class so I was at least trying to answer you before I forgot my thoughts. It's sad that myself and other fans of the show and Mari have come up with a better plot and more development for her than the show ever did, but that often happens a lot especially for characters of color. It's so bad, how Mari was treated, that I have a fic waiting to be made to give her more justice. I don't even think I'll tune in for s4, largely because of the treatment of the poc characters but also just the direction of the show as the writers have now admitted to just focusing on theories and doing whatever they want. This is big because I usually can stick around and/or come back to a show, even with some questionable and critical elements (eg. The TVD series and its spinoffs). But that doesn't necessarily mean that it isn't sad or disappointing, especially with, as you said, the current political climate (killing off most, if not all, your Latin characters and having a brown girl, Crystal, be killed just to serve as a plot device for Misty, a white girl, is not great) and how stereotypes can be harmful, especially towards poc (Simone being reduced to the "disposable black girlfriend/partner" trope, Tai's storyline revolving around yte characters, just to name a few). The Yellowjackets are in the corner, shaking hands with Julie Plec (J Plague) and Stephanie Meyer, which isn't good at all.
