This is an interesting observation, and I think I've seen it around too: in pushing back against (more common in the early fandom) "boring leader" stereotypes, sometimes people do over-correct Leo into anxious woobie territory. Heck, I'm probably a bit guilty of this here and there. I love the tasty drama when his confidence takes a gut punch as much as anyone, but it really works best in contrast to his self-assured baseline. There's a lot of stress involved with being the the one calling the shots, but I think Leo generally thrives on this (or at least feels like he does - they are teenagers continually getting dragged into various flavors of gang war, which is... not ideal).
He shouldn't be an arrogant jerk overall either (which is the other extreme from "boring" that Leo-dislikers have traditionally run with), but will have some Moments as his level of confidence conflicts with his level of capability, or as he projects his perfectionist standards onto his brothers.
Not the same iteration of Leo but very similar so I'll include it as an example of what I mean by Leo projecting: the reason I hate his "I'm better than you" line in TMNT (2007) is not because it's unrealistically mean or arrogant in this tense moment, but it misses Leo's mindset. Sure, frustration is boiling over, but remember this guy just slunk home with his tail between his legs after failing to achieve his training sabbatical goals - confidence is not riding high enough for that kind of declaration. Leo perceives that his brothers have been slacking as a team in his absence, Raph being particularly disengaged. The front half of this same line of dialog is an attack on Raph's flaws, which is a good fit for his headspace and the flow of the argument. Instead of the swerve to "I'm better than you" though, I'd have him finish somewhere along the lines of "at least I'm trying," which is about as damning an accusation as Leo knows to give. It's also guaranteed to sting Raph, who is putting a lot of effort into solving the problems he feels Leo left behind, actually.
(Now that I think about it, this "why am I the only one putting in effort" complaint is basically the root grievance 2k3 Leo keeps lashing out with in his season 4 spiral, though obviously the two situations are pretty different)
(aaand a little side tangent about non-leader Leo I've been chewing on for a while, that I'll just tuck under a cut here~)