no tank game

Yes.

Tanks are so strong right now there is no reason to play anything else.

Of course. U have even higher chance of winning in lower than plat elo without tank.

if the enemy team is absolute shit compared to yours

While it is possible to win with no tanks, it is extremely difficult since everyone on your team will be squishy.

Tanks make it easier for the squishy teammates do their jobs by them soaking up all the damage for their squishy compadres.

Possible, but much harder. Without tanks (actually, only some particular tanks) your engage will be pretty bad. Also, the peel should be pretty bad too as there's no one to cover movement paths.