Regardless of what the numbers say, it feels bad to get eviscerated in 2 seconds by a single champ as a tank. I come from PC League where tanks feel pretty alright right now (still not perfect, but they live WAAAAAY longer than in WR). I find it better to build tanks full damage. At least that way I actually do something before I die in the same amount of time.
This feeling is the part that really matters here. Tanks can be strong without feeling tanky enough and that is totally valid. We would like to adjust how this feels, I personally have felt plenty durable when playing tanks (typically Rammus), at least until the very late game, but that doesn't mean they are weak.