Even the core aspects of combat could be addressed in a mod. Dependend on whether TW let's modders "go there".
I think the ydefinitely will. They have stated that they want to make it as mod friendly as possible and at least as viable for modding as in WB. So yea. But no matter if there is a good modding api or not modders will and can mod anything. Minecraft has not had a proper mod support since years and there are so many huge game changing mods. Same with many other games (GTA, Skyrim etc.).
And regarding the intial post: I have about 2,5k hours in MB and I think we should give them the time to sort out all the things that are criticised and reported right now. Be happy to have a playable release and I can also acknowledge their effort with all those patches they have been releasing.
I actually don't care about the class selection that much. Mods can change it anyway and it's not like you have no customization at all. Who knows maybe they will change it in a future update or just add more options to it. I don't think that having balanced classes with perks is too bad for a normal multiplayer experience.