Problem is not only the encounter difficulty though, 2h/dw+warfare drastically overperforms compared to other skillsets, so it's impossible to balance the game for them at the same time.
And yes, progression is important, but becoming OP in the endgame is not a given even though most RPGs suffer this fate. However some do manage to pull of a proper difficulty scaling.
Your first point is true, but by putting some barriers to keep those synergistic effects from maximizing everything, balance would at least seem more fair. Of course, the skills and talents, still need some balancing; I just don't think thats the be all end all of it.
As for your second point, well, you're not wrong, but those are more outliers than not. Any minmaxed build optimized well is gonna grow in power in an rpg exponentially over time....other builds are more linear in growth. Trying to account for two very different growths is hard.
This isn't really a problem though cause being OP end game at the last couple fights where you can lol through mobs is a fun reward to finishing the game in its own way. In game one we're basically gods anyway so why question it?
If they want to keep difficulty consistent without annihilating more casual players in order to account for end game min-maxers? I don't really see how this can be done without having various versions of enemies (if not flat out level scaling), special events, or optional content geared towards the min-maxer