Overloaded kits can lead to problems that are unable to be solved due to the fact that the game is ongoing and always current, whilst champions are not ongoing and current until a rework or a buff is made.
When a developer makes a champion, i would assume the thought pattern includes the following. Keep in mind, this would be the mind set of when the game is being developed and only has about 50 or so champions.
"So what if this big burly guy, did not react to any crowd control? Like he could just completely ignore everything and hunt down the adc, adc's have a tendency to not have very much mobility and rely on tanks to protect them, kill this champion before they kill your carry. And he can have an attack speed steroid that allows him a little bit of regeneration, that way he can be in the top lane and jungle! He can throw his weapon, lets see an axe! And the axe obviously will slow down the opponent is hit, and he can pick it up to shorten the cooldown! It makes sense and everything, Concluding the fact that one of his abilities allows him to attack really quick, we can give him a passive that when he gets hurt he can attack faster and faster! One of his abilities scales with each attack, we can give it true damage but low scaling and forces him to interact."
Now this is NOW this is how i think CertainlyT makes his champions, his thought patterns and even the new developers? If there is new devs?
"So what if we had a support, who is like a living spirit vacuum and lives in the shadow isles? He has a chain that he drags around and uses it to drag people around, he also has a lantern that contains all of the souls he has stolen and contained. He can throw out his chain and drag his enemy back, multiple times too, and decide if he wants to pull it again to launch himself towards the caught enemy player. He can also use his chain to disposition the enemy, send them towards himself or away from himself, and it allows him to poke, and it scales with time, and it scales with ability power which scales infinitely. Also, he can throw out his lantern to shield his allys, even the entire team! This also scales with his ability power, which scales infinitely, and one ally can grab it to reposition, it can be used as false bait, real bait and assisting with ganks! It can ward a bush so he doesn't get caught out and just about everything any support could ever want! And his passive is he collects the souls of minions, enemy and ally champions which he scales from for ability power and armor. His ultimate has perfect synergy with his Q and slows down the enemy for 99% of their movement speed, it hurts them, multiple times too! And it can zone, and offer large amounts of CC and is about the size of the river, and-" Woah woah woah, hey Mr. T you are really imaginative! But uh-uhm . . . i think that is enough.
". . . I mean he has to pick up the souls."
TL;DR
Well designed champions do not need overloaded kits and a bundle of free stats to actually become a viable champion. If you look at his champions alone, you can SEE that all of his champions have balancing issues. The exception being Darius, i'll give him that. TerribleT is an AMAZING champion designer, but making every champion overloaded that he creates will not make the game fair for champions with normal kits.