this does not change anything. isset is not a function in PHP. and both codes are generating exactly the same opcodes: https://3v4l.org/ZvRAY/vld#output

So I suggest keeping the existing code, which is more readable IMO.

It's true that this doesn't save any function call. My bad!

If you don't think that the new version is more readable, let's close it. Thanks!

Well, with 2 arguments, people have to remember that isset does a AND. With the existing code, the operator is explicit. So this makes it a bit easier for people not remembering the exact behavior.
Note however that my preference would not be strong enough to make us change the codebase if we were already using the combined version. But I don't think switching to the combined version is worth it.