Currently, the majority of these champions are in the "shit tier".
No, they aren't.
The majority of those champions just aren't the most popular champion for their given lane.
Look at it this way - if you want to be the best, are you going to practice using the strategy the guy that came in 12th place used or the gold-medalist's strategy?
Even if this is swimming and the guy that came in 12th place was only 0.5 seconds slower than the guy in first, everyone's just going to default to the #1 strat.
Also: pros don't need an obvious valley in power disparity between 2 champions to make a decision on which one is better. If one thing is 0.001% better, a lot of pros are at a level where milking such a small advantage is why their win rates are ~80% over a typical 50%.
And that's why you only tend to see the same ~15 champions over and over again in tournaments. To Riot's credit, they usually balance things well enough to create a rock-paper-scissors dynamic between the top 3 picks of any given lane position so you get a bit of gold/silver/bronze action for each position.
Most of the champions you listed regularly boast monthly win-rates in the 50%~52% range. Not being one of the ultra-popular ~15 must pick/ban champions doesn't make a champion garbage. It only means the meta doesn't see them as one of the top ~15 champions.
Many meta shifts and regional strategies tend to hint the best ~15 champions in the meta aren't truly the best ~15 champions as well, you could easily be listing hidden OP picks up there.
So no - those aren't shit tier champions.
Like what was said in the Patch Rundown, we need to avoid "Olafing" champions. Many of these champions have been "olafed" and need attention.
Olaf's nerf came after he saw a reasonable performance at season 2 world's. I didn't really see him pull off anything more impressive than the other 2 predominant top-lanners of that year, but Riot decided to go overboard on nerffing him.
Olaf only had something like a 46% win-rate (monthly, ranked 1v1, 5v5, and normals, bronze through diamond) before he got hit with the nerf as well, and Riot removed Force of Nature at the same time.
Abusing FoN while having a decent lanning phase against the other 2 meta top-lanners seemed to be the main reason pros were running him.
In the aftermath of Riot's nerf, Olaf came into season 3 with one of the lowest 3 monthly win rates, and stayed that way for months.
When people say "Olafing" they don't mean "not one of the ~15 most popular champions", they mean "overnerffed into an unplayable state on every front".
If your list of Olafed champions consists of more than ~6 champions, you're probably doing something wrong.
I'm sick of seeing the same champions every game.
I'm pretty sure everyone is - but seeing the same champions likely has nothing to do with balance.
I'd say that's mostly psychology.
It's the gold, silver, bronze, nobody has room to care for 4th place mentality.
Outside of god-tier balancing or a massive incentivisation for player experimentation, I don't see LoL's meta-game ever giving up a top ~15 best champions structure.
Even with world-class teams pulling off picks and having a massive champion pool steamrolling teams clinging to the best ~15 champions, the meta has always stuck to it's guns with a best ~15 champions.
If Riot did something epic with champion-specific achievements pushing players to utilize champions for their optimal strategic, tactical, and reflexsive play-patterns on a champion specific level, -maybe- you could excite and educate players in a fun way about the strengths and weaknesses of each champion.
Perhaps enough to absolve the top ~15 dynamic and give players the knowledge necessary (in a very heavy burden-of-knowledge game) to select champions and team-comps with greater ease, without having to fall back on a small handful of picks.
I don't see buffing (or nerffing) champions ever realistically creating more champion diversity.
for example. Some need full kit reworks 
for example. Some other champions simply need some buffs to stay relevant 
for example. Feel free to discuss any buffs for any of these champions.
