let's make the quest stories of ancients & lunar completely void of anything shall we? The story clearly tells about the choice of different means of living to get to lunar/magic levels. It is indicated quite often that you can't use lunar magic while not being "enlightend"... Don't forget that roleplaying is still a large part of an role playing game.
Yes, let's. I think it makes no sense at all, and it certainly doesn't work for the combat triangle - giving up virtually all magic ability to be able to farm properly? Giving up all enchantments just to be able to mage properly? Farming, enchanting (smithing!) and combat are not things that should be mutually exclusive in any way.
In the end, we only pray at an altar to switch spellbooks. There is absolutely no 'different means of living' (I think you mean ways of living?) - people on lunars can still massacre non-magic bosses plenty well, and they do, and it doesn't affect their ability to cast lunars at all. It's more likely that the Moonclan firmly believe that pacifism is required for Lunars because of historical/ideological reasons, and you, as outsider, come in and have no such compunctions about using combat magic with lunars. Sure, the Moonclan may not like it, but who cares, you got the spells, no need to enforce that pacifism on players.
Now Ancient Magic, that's different, because Zaros actually affects you directly, but there's no reason he couldn't give you access to Ancients while keeping your normal spells intact, it's just a matter of convincing him you're worth it (there are probably some magical secrets you can figure out combining Ancients with modern magical insights).