Mao is very strong early due to a gapcloser + 3 kinds of cc pre-6. However, he falls off really hard late game. His base damage is relatively high, his skills actually are on a pretty high cooldown with the exception of his short range, weaker Q (13 seconds is really not a low cooldown for a gapcloser at all) and he just doesn't put out that much damage for whatever reason. Also, his ult is never big enough to cover many people; generally you're either covering your backline allies (in which case its rarely going to damage opponents), or a couple of melee range champions (in which case you're reducing damage to your allies who are usually the tankiest anyway and dealing damage to the tankiest enemies). He can engage on enemies caught out of position well with his w and start off a teamfight strong, but all he does after that is heal and tank, but nobody focuses him so it doesn't matter that much (at least, this is in my experience). He's still good because of his great ganks early, but he falls off late-game hard imo.
