Ekko, Fizz, Garen, Graves, Irelia, Nasus, Nunu, Olaf, Renekton, Shyvanna, Trundle, Udyr, and Vlad are not tanks mate.
The balance of defense, offense, and utility has not once actually been balanced in the history of League, so I'm not sure what argument you're trying to make here.
There are currently two types of defensive champions that are popular, high damage carries who can deal their damage regardless of itemization, and tanks/bruisers who can absorb the high damage being output from carries.
The high damage carries like Ekko and Fizz are in need of balance changes, no one is going to argue that.
The tanks and bruisers, however, are not actually unbalanced. They are popular either when tank items are overpowered (like we saw in the past) or when carries have very high damage (like right now). Resistances mean little to nothing, and since most mixed offense/defense items give health, which is still fairly effective even with all the shreading, champions who can use these items are popular.
This isn't a tank meta. Tanks are popular because it's a damage meta.