Limiting StarFleet officer’s flaws because they are models of heroism in the series is an interesting point of view and makes sense. However we could imagine officers with many flaws who are still heroic individuals: arrogant, devotion, enemy, pacifist, reckless, rival or species enmity or flaws an officer could have without contradicting the exceptional nature of Starfleet officers. As far as I’m concerned it’s just that I think it’s better to build a character around a few strong points (positive and negative) which stand out clearly, imo it gives a character more flavor than allowing many edges/flaws. But that’s just a personal opinion.