So? It's "easier". Ok. You seem to think it's one way or no way.

Why cry about it when you don't want try a different way? There really are only 2 real reasons why it's perceived to be easier with just archers and mages: 1) range; no huge spikes of AE dmg since they aren't in melee range which results in no upkeep of healing except on the tank 2) Archers are the fastest-most reliable burst type classes and mages have the most OP form of damage in the game.

Completing a speed-run is more about time efficiency more then anything, as well as good communication and understanding. If you're dieing on the way, or killing things you shouldn't be killing, killing things much slower then you should, etc. then you're going to have problems completing it even with Archers and Mages.

Melee do perfectly fine in speed runs. You just have to be confident and competent with your group.