Tank Ekko was considered unhealthy, Tank fiora is considered as unhealthy
...can you do something with tank Yi?
...can you do something with tank Yi?
Next on the list

EDIT: Looking at the direction of the debate, I'll just note this was but a joke. I haven't played as or against Tankali, so I am not complaining. I am simple creature. I've seen "unhealthy" and "tank" in one sentence and my inner flame wanted to drop down a Tankali joke, since it became more popular now. I love you all.
It's a matter of gameplay direction, Ekko was supposed to be an assassin, high-risk, high-reward, due to how high his values were, he could go tank and perform a low-risk, high-reward kinda thing. He had the tools to go all in and then get out, which combined with efficient tankiness made him too safe.
Fighters are ALWAYS supposed to be able to gauge their power between their damage and their tankiness depending on the situation, since they have to do their job in the enemies faces without having as many safety tools. Right now Tank Fiora and Tank Yi are only a thing due to how bursty the meta has become (This is entirely due to the prevalence of thunderlords and the nerfs to defensive masteries). They have to get defensive stats in order to do their jobs properly, and they do them a -bit- too well due to their targets having absolutely no defenses (since it's inefficient to build some defenses when everything is getting blown up instantly).
Even if we nerf them, it'll only open up the place for the next light fighter to take their place by beefing up (until they're all nerfed to the ground, and then we have an entire class rendered useless, like the extreme tank nerfs after the cinderhulk meta). It's a meta problem, and Riot has to look into how bursty and snowbally the game has become.
Tank Fiora is far more cancerous than tank ekko
'Tank' yi needs at least 2 damage items to do anything at all.
getting 2 shot by someone with more then 3K health and at least 250 armor/Mr isnt really a balanced game experience.
Eh, big difference. Yi and Fiora don't bring team wide utility like Ekko did, all they really have is their damage. It's an issue, aye, but not nearly of the same level/
It's not tank Yi, it's bruiser Yi. A tank build does not have more than 1 damage item.
If you want to see actual tank item abuse, looks at Akali top or release Ekko
Yep. Nothing fun about getting cut up in 2 seconds by a guy whose health bar looks like a Mundo.
Tank bruisers is as old as bruisers themselves and only considered a problem in the context of the fighter problem.
Tank Ekko was different, he's technically an assassin that requires precise set up. Going tank meant he didn't have that problem.
Don't forget tank 
Tank ekko wasn't considered unhealthy, it was considered a little too strong and thus toned down. Unhealthy implies a gameplay pattern that detracts from the fun overall, which is what fioras tank build currently does.
Dont forget Tank Akali!
Tank Akali is so gross...
Its more about how strong and cheap a couple items are.

he still has the problem if being locked down and dieing instantly even tank yi he does way less damange and wont insta gib you unless super ahead. full assassian yi can 1v5 fed a fed tank yi can only get about 2 kills and u still have low base health armor and mr so any sort of cc against dmanage and your still ganna die pretty fast just not as fast