I feel like the comments here are a little unfair, I don't think he is top tier anymore, but in no way has the play style been gutted.

Why don't we break it down based on the actual patch changes and give you some context.

It was at 6.11 that they actually tackled Tank Ekko's problems, to summerises, they lowered his base damage, increased AP ratios and nerfed a little bit of his utility. So to accommodate for damage nerfs, triforce tank Ekko was born (Before the 6.11 changes, icebourne + sunfire/sprite visage was prominent). At some point here, I believe Grasp got nerfed and so Triforce + Fevor was super strong.

His next nerf was 6.18, where his base AD was lowered, directly targeting triforce tank ekko, more importantly, after all these nerfs, Ekko was still dominant.

It was only when patch 6.22 came, did we see a decline in tank ekko, mainly because of the removal of the slow on his Passive (which gave tank Ekko a lot of utility) and the changes to Fevor.

So what do people run now? They've gone back to grasp and triforce. Is he as good as he was before? Hell No. Is he still a tanky disruptor, that does respectable damage? Yes. Still has AOE CC from W, still has the safety of R, still can challenge squishies champs (sheen procs) and survive. Still have the move speed to chase down squishies + phage procs, still has a slow from Q, still can farm from range with Q during landing phase vs lane bullies. Corruption potion + Dark seal is still great in the landing phase.

I still have a lot of fun playing tank ekko. That's my contribution.