It’s based on position, yes, but there is a reason it is called a tank and a reason why you need to be selective about who to place in that position. It is called a TANK because it is supposed to be a strong hero who can absorb a lot of damage (think of an actual war, you want to put the heavily armored units up front to take the brunt of the gunfire). Because of the way the tiles work in the game, the tank is going to get hit the most often. You want your tank to absorb those hits while remaining alive as long as possible, giving your flank and wing / corner / edge heroes more time to strike without getting killed. The heroes on the far corners are generally going to get hit the least often, meaning they won’t charge mana as quickly, but they should ideally survive longer (depending on boards and your hero setup).
I don’t have any of the fancy 5* heroes you have, but I will say that you probably shouldn’t put Wu Kong on a defense team unless he is your strongest yellow (and even then, you might want to substitute a different color if possible). Wu Kong can be phenomenal offensively, when tiles are in play, but defensively, he’s squishy and prone to make your other specials miss (which you do not want to happen on a defense team, since special skills are your primary form of defensive attack).