I'm not going to talk about the bigger issues already mentioned by others here (ie: balance, people cheating, ranking, etc). Here are some very minor low hanging fruit improvements that I think would make CC a lot better:
1. Some moves need better clarity on friendly vs enemy attacks. A big example is the SMN wind DoT on the ground. There's also the SMN bahamut (which SMN has baha up is unclear) and the DRG LB (if both drg do the LB which one is the friendly).
2. The icon for Guard should change once it's used since in the middle of a big battle with a lot of CCs it's sometimes unclear if you used it or not as it is hard to see. But if you did use it and you press it again it turns Guard off which may not have been the intention. There's also certain situations where Guard at the same time as some CC puts you in the Guard animation but without the bubble. This is kind of confusing, was the Guard put up or not?
3. The starting screen (right before the portraits) animation should be sped up, that's like 20s of wasted cutscene time. I'm not talking about the portraits themselves, that's fine. Just the transition screens and the zoom around the map.
4. Picking up the choco feather's timing is a bit too tight, sometimes I'm dead center in the middle of the choco circle and it still doesn't give me the feather.
5. On the fire map the bomb shouldn't be able to hit you while you're still running out of the base.
6. The roles should be balanced in matchmaking. I know the roles technically don't matter, but you can never perfectly balance each job/role, but you can at least make it more even if both sides have the same number of melee/ranged/tank/healers. It's really frustrating otherwise.
7. Plat 1 players should not be able to be in Crystal games. Neither should Diamond 5. Ranking up is just too easy and the skill disparity between some high Crystal players with low diamond players is too big.
8. Diamond tier should have no streak bonus, and probably needs 7-8 tiers. Crystal is way too easy to zerg into.