Well, I'll need you to give me a list of CertainlyT's champions to make an accurate response here - I looked for one but I think it's incomplete as there were other champions he's been blamed for that weren't on that list.
Also, my response was largely meant as informative - i.e. not my own opinions but a collection of what I've read in complaints against CertainlyT's champions. Meant to explain to the OP why people dislike his champions and hate on him more than the other designers.
To give an example to answer your question though: Yasuo.
He has 2 passives - double crit (which could be an ultimate in its own right), and a periodic shield which is powerful in its own right (although it does have counterplay).
His Q: Basic ability is a short ranged linear skillshot. Added effect, stacking twice results in the third doing something different (a knockup). Added interaction with his E, changes linear skillshot to circular AOE. Added cooldown mechanic - reduced cooldown based on bonus attack speed. (note, that's already 4 components in his first active skill).
W: Wind wall, blocks all projectiles on an instant cast. Not that it's a bunch of effects, but could arguably be an ultimate (I mean, it negates a lot of ultimates... AND can protect not only himself, but his team).
E: Short ranged dash. Extra effect: Can dash to additional enemies if they're there sequentially. Additional effect: Damage increased on successive casts.
R: Blink (like flash, instant dash rather than just really fast) and do loads of damage. Additional effect: suspends them (basically prolonged knockup). Additional effect: ignores 50% of bonus armor for next 15 seconds. Additional effect: generates maximum flow.
The only skill in his entire kit that comes close to "normal" is his E, which is limitless dashes. Like seriously, that alone is normally something a lot of people complain about. So even in a state where he's balanced and has weak match-ups and can be beaten, he's still going to be annoying at best. His wind wall just infuriates every ADC. His Q and R seem overloaded.
It doesn't mean he has to be OP or can't be balanced, just that he becomes fun to play as, but unfun to play against. That's a recipe for disaster, a popular champion that no one wants to play against even if he's weak.
, and that definitely calls his champion designing prowess into question.
(rework) 
. Is it really fair to bash so much (and often exclusively) on CertainlyT when you look at what the rest of Riot has been up to?
and 
and 
. He puts out as many interesting champions as infuriating ones.
and 
are all BS champions that should be added to the list. Hell, every champion should be added to the list for that reason.
