The ones that couldn't win so they had to make themselves look better by giving themselves some sort of unfair advantage by making rules outside of what was already established.
He can't design a champion within the already established structure of the game so each of his new designs have to break some rule that only he gets to break when designing champions.
Zoe = terrain lengthening skillshot, RNG use of other spells and items
Akali = obscurity
Zyra = plants (on release her after death shot)
Darius = true damage resetting execution ult (the true damage part was unique on release)
Thresh = infinite scaling souls passive
Yasuo = 8 passives (hyperbole obviously), projectile blocking
Graves = shells mechanic (half taken from Jhin but somehow made more complicated)
And on and on with all his champs. Every single one has SOME sort of design that just throws the rules to the wayside and makes up a new set of rules on top of being overly complicated and muddying the waters. Look if you think he's a great designer that's certainly your opinion and you're entitled to it. But let's be real, CertainlyT is creative in the way that annoying kid in grade school was who constantly had to change the rules of the game.
TL;DR - CertainlyT is Cartman in the episode of South Park where they play ninjas. Every time someone has an ability more useful than his he has to come up with some new ability that is better than the last persons.