I am not hyped at all for season 3 mechas because I liked to have the choice of who I want to make.
But that changed now with those mechas... They're kinda obligatory to stay competitive in the top ranking, at least in Korea.
In this pic (below), do you see the black borders around the portrait ? That represent the character who got a mecha.
Pic with a full team of mechas in arena : warrior, rogue, healer and paladin.
They can even be used on WB.
Here, we can see a team of mecha in the new pvp ground (some kind of attack player base and defeat his 3 waves of allies)
Another screenshots of how much meta team matter in in the top % of arena in Korea.