I assume you mean that employees who think their colleagues must suck at Y because they are on team X, or who worry themselves about whether some other team's chosen hiring standards are "too easy," are the immature ones?
(And presumably it's immature to even care about 'sucking at Y' at all, unless a specific task requires skill at Y and is not being solved, in which case it sounds like a problem of assigning it to the wrong person, not a problem of general hiring for Y in all cases.)
(And presumably it's immature to even care about 'sucking at Y' at all, unless a specific task requires skill at Y and is not being solved, in which case it sounds like a problem of assigning it to the wrong person, not a problem of general hiring for Y in all cases.)