I do not agree with your "investigation".
For starters, you didn't cite any of the sources, all you said was "So speaking with coaches from various elos", which is not a very inspiring thing to start off with, because most coaches don't know what they're doing and the ones that do are trying to force information into the wrong elo which will make the player they are "coaching" even worse.
You said you talked to "challenger" players, which makes me think you just gave some random twitch livestream question like "Is top lane a bad lane right now?" and they answer with "yes", leading you to believe you just got the scoop of the century because 1 challenger player that might not even main the role said yes to your question.
Meanwhile in no part of your post did you say who it was that gave you the information, so the legitimacy of the "sources" cannot be established.
As for your own personal experiences, top lane has been the dominant lane through most of the seasons. Having a few seasons where top lane isn't #1 is going to happen. Another factor is in the changes the game makes over time. Item changes, new champions, reworks, everything that touches the game touches every single lane. This season we've had champions like Kled and Camille rolling through top lane, Fiora dominating everyone with her true damage, so it's safe to conclude that top lane just hasn't been favorable to you specifically this year. Meanwhile I've been finding some good success with standard top lane champions like Trundle and Renekton lately.
Finally for the champions that "shouldn't be in X lane". Quinn, Karthus, Kayle, Heimerdinger, Annie, Cassiopeia (fixed Cass's name for you here) going top lane we'll begin with. I'll go over these one at a time.
Quinn : Ever since her release, she has been used top lane as a lane bully more often than any other role except for possibly jungle. I'm not surprised when I see her top lane ever because of this (I'm a season 3 vet, I was here when Quinn was released).
Karthus : If someone is losing to Karthus in lane, then that problem lies with the player not the enemy champion. A Karthus in top lane is an extremely easy and free lane, especially once you get a little MR.
Kayle : She is used as a top or mid laner rather commonly, swapping based on metas. Another champion I'm not surprised to see top lane, just annoying to fight her when she is there.
Heimerdinger : Another Kayle case, but is more often seen top because of how low of range most top laners have, allowing him to zone and push with a good amount of safety in the early stages of the lane phase.
Annie : The only player I ever see take Annie top lane is Annie Bot (who is for the most part an Annie 1 trick, if he doesn't get her he uses Malphite), and I've watched a lot of top lane matches because that is my #1 lane.
Cassiopeia : Another case of Karthus, where if you lose to a top lane Cass the problem is with the player because of how easily she gets walled by MR.
Now for Swain, Vlad, Jayce, Gangplank, and Renekton going mid.
Swain : Another champion that swaps between top and mid commonly.
Vlad : Another champion that swaps between top and mid commonly.
Jayce : A champion that goes mid based on who the opponent is, if it's an immobile mid Jayce is usually used because he can abuse them.
Gangplank : Usually used vs melee mids due to his barrels being good zoning tools, less effective against Zed but still used regardless.
Renekton : This one is an unusual pick for mid, mainly because of how he is played (Renekton is one of my top 2 champions in the game, so I know him very very well). Anything with mobility will be impossible for him to kill and anything with mobility + range will be pretty much a lost lane. So Renekton being better mid instead of top seems rather unlikely.
I hope you found my counter points at least entertaining to read, and hopefully next time you clean up your information where it can't be so easily picked apart.
