More specifically, these champions 
. All 5 of these champions have sub 47% winrates, and extremely low playrates.
Please don't downvote because you hate any of the above champions; because that's counterintuitive to a discussion.
Caítlyn1 votesYou forgot 
Masala Chai1 votesBut they aren't that bad, sure they're on the weak side; but no one will go "report kindred troll champ"
JavelinJoe1 votesThey will for 
and 
though.
R FLASH XD1 votes[{quoted}](name=Full Moon Ace,realm=NA,application-id=3ErqAdtq,discussion-id=j5m51d6R,comment-id=00000000,timestamp=2016-09-10T06:09:57.322+0000)
But they aren't that bad, sure they're on the weak side; but no one will go "report kindred troll champ"
Well I don't find Azir a troll champ, not Corki. maybe Kalista, not Ryze and definitely not Talliyah
legionnaire991 votesIf you take the time to learn them there winrate a skyrocket and the rock chick was strong in solo q
GULAG 4 U1 votesnerf em' into da ground into trollpick tier
What they've been doing for seasons now
PermabannedGaren1 votes[{quoted}](name=Full Moon Ace,realm=NA,application-id=3ErqAdtq,discussion-id=j5m51d6R,comment-id=,timestamp=2016-09-10T05:16:29.758+0000)
More specifically, these champions
Please don't downvote because you hate any of the above champions; because that's counterintuitive to a discussion.
None of those champions were nerfed solely because of competitive except maybe Taliyah (Ryze hasn't been nerfed at all since his recent rework).
They were incredibly strong in solo queue too. In the case of Azir, Kalista, and I guess Ryze's prior version, this was mostly the case in very high elo solo queue.
Plat+ champion.gg data is not always a good demonstration of a champion's strength. Rek'sai has consistently underperformed on that site, but was still a highly contested pick in Masters/Challenger, because she was extremely powerful though.
No, a good example of what you're talking about is Shen, who wasn't used particularly often in even very high elo solo queue but still got heavy nerfs anyway.