Morgana isn't really a support anymore either. Her WR as a support has plummeted and most challenger support mains seem to say she's garbage tier beyond a counter pick. This seems fine to me. She was originally released as a mid and she, along with all the other mages, are strong in mid lane right now.
Tahm probably had a less well-defined initial role, and while he may have been a support pick in the LCS or high level play, he was generally not picked at all. Now he is the terror of top lane. I think it's healthy that he gets to finally be good at something and be picked.
Honestly, Riot needs to give up on the LCS. It is destroying League. The decision to make stopwatch timers longer, and remove Tahm's ability to eat an ally, and nerfing black shield, are all indicative of Riot wanting people to get kills in laning phase. Unfortunately, this turns League of legends into more of a brawl than a strategy game. I find it quite annoying.
I'm perfectly content going into my lane and farming minions, strategically warding, and rotating to objectives and gank. I don't see the need to make sure that burst assassins and dive champions excel at killing people. Dive should be a risky strategy. Right now it seems to be the only strategy that Riot games wants to allow. It's disappointing.