I honestly don't think the game would be finished without some core graphical elements.
Sure cosmetics like custom decals can wait. but major structural changes to mechs should be represented in my opinion.
I'm curious as to whether you had severe difficulty enjoying any of the past MechWarrior games, because they all had this same issue. MW4 had it mitigated to a degree because of the slot system it used, but still, if you dropped an SRM-2 in a Timberwolf's torso, the launcher didn't change in shape and size. You just had a 21-hole launcher that only shot two missiles.
I agree it's a bit silly not to see weapon changes, and it's definitely better for immersion to see your loadout changes reflected on the 'Mech, but I don't know that I'd call it a core graphic element that the game can't launch without.