Even Swen admitted the armor system was a mistake. Example: A mage on the Infinity Engine games is easier or harder to defeat by another mage (magical damage equivalent) or a fighter (physical damage equivalent)? The answer is depends on the mage's spells and the fighter's weapons, the system created by Larian doesn't allow for such subtleties, pretty much when you see a huge magical armor bar, you knew the right answer was to use a physical attack, period, and many times which to use was kinda superfluous, just the one with the biggest damage (the result of making defenses working like HP), that is predictability and I find it boring.
It still depends on a mage's spells in DOS2. Y'know, Necromancy does physical damage, and Geomancy or Polymorph skills grant a lot of physical armor. So it is not necessary that a mage is worse to defeat another mage. As for "fighters", they're not limited to physical damage -- despite being admittely less flexible on damage type then mages in DOS2, especially for melee types. Fighters attacking at range have ways to make attacks of any element, have special arrows, and piercing attacks, etc. When it comes to melee, the Scoundrel tree has some attacks against magic and some piercing. The Warfare tree is more limited there and must appeal to something else to supplement it magically, such as Geo for venom coating or Pyro for sparking swings. But it's true it's less obvious to make a melee fighter that does mainly elemental damage; there are a smaller number of viable builds, and no purely elemental melee weapons.
As for the idea that combat is boring and repetitive because you just try to do damage, I don't see it. I find myself rarely choosing attacks because they do the most damage. I usually am setuping future moves, surfaces or circumstances to combo off of. I often choose attacks that CC the enemy or do some effect, because effects are better than just pure damage, unless it's a killing blow. The Scoundrel tree for example has nice things: Rupture Tendeons hurts the enemy if they move and applying it bypasses armor, being able to set atrophy or decaying is great, decay especially is great to turn your healing spells into attacks, etc.