I'll follow your advice and quote you here to avoid derailing the other thread (again).
Tuco's post in that thread best illustrated the problem in a succinct manner.
Excuse me that I only quote this part instead of Tuco's post fully, I do it to avoid making the post too long (it is long enough already).
Tuco point out quite well the issue of the armor being in a way an extra HP bar that must be erased before being able to do CC, and that once is broken CC is pretty much all that matters. My response, I'll be honest, is going to be considered quite poor. While I can see how you and Tuco may consider it a flaw, I actually find the system fun in its own way. Putting aside balance problem with the power of the skills, I find that the systems encourages both to maximize damage and to make a "responsible" use of your skills. This is because many of the same skills that deal damage also are used to perform CC. Due to the cooldown system, this creates a choice of when to use each skill and to consider the risk and benefits of doing so; "Do I cast Electric Discharge to damage my opponents, or wait until its armor is off to Stun them?" Then you have to add many skills that either target armour itself, feats that allow you to inflict certain status effect on enemies despite having armour, and skills that outright let you hurt enemy HP despite having armour. Then you have more powerful spells like Equalize and Exchange Vitality, so there is more nuisance and strategies than just damage. I know this answer pretty much amounts to a "I like it", but the same issue Tuco points out I didn't find it that problematic simply put because I enjoyed the idea of maximizing damage while protecting yourself. Is not a system I want in every game, but I did find it to be unique and fun and wouldn't mind the idea being more worked upon in future Divinity titles (if BG3 doesn't end up ruining the company).
The thing is, because of how unbalanced the system is, the fact that it encourages stacking a single damage type (to be specific, physical is heavily favored), isn't really that noticeable. There are many powers which will outright 1 hit enemies (its surprising this game isn't Victor's wet dream considering how OP the necromancy spells are) and in order to bring any semblance of balance to the system, you either need to avoid whole swaths of abilities, or you need to mod the game a bunch.
From memory, there were only 2 or 3 enemies in the entire game which had physical resistance, the player clone during a dream sequence, the bat voidwoken and some of the creatures in the consulate. In contrast, most enemies in the game had resistances to 1 or more type of elemental damage and the resistance values were not low, sometimes going to values which would cause the powers to heal them. Yeah, it ultimately did not matter because damage values even post resistances to all damage types still far exceeded HP totals, but that doesn't mean the problem was not there, just that the system disguised it.
I agree with this, but I think it was more of an issue with the balancing of the game and the enemy design than of the armor system itself. Probably by balancing the HP and Armor Values and the resistances of the enemies and trying to reduce the power creep of later levels you could solve these issues. The problem lies with the stats being just increments of damage and being able to gain so many as the player levels up. Yet again, I agree, the game had balance issues specially on the later half of the game.
To play a bit of devil's advocate however, there are ways to work around this in the game with skills like Flay Skin which reduced enemies resistances a 50% and destroyed Magical Armour, which was great on Martials as it scaled with STR, and you could use it to support the casters. As well as skills like bleed fire allowing you to reduce even more resistance to fire spells. Also to the damage of spells, things like the burning and poison status effects should be taken into account, as well as surfaces, which mages were the masters of creating and controlling, which added to the overall damage potential of mages. Talents like Elemental affinity and Torturer further improves mages damage potential, allowing, as I said before, to inflict damaging status despite the enemy having magical armour, while Elemental affinity reduces the AP costs of casting spells, which is incredible valuable and greatly increases your damage per turn.
Also a lot of these claims also seem to ignore the fact that you have to go through the first 2 acts first before reaches those levels of power. I had seen people said that you should go full magical at the beginning and then full physical after a certain chapter or level. This I find an indictment more on the players than of the game itself. Not so different, for example, of building your Pathfinder KM team to deal better the enemies of an specific chapter and then using the respec option to change them to another specific build better suit for the next one. It requires meta knowledge of the game and it works so well due to the easiness of respecting characters in the game instead of any flaw on the system itself.
Despite this long rant, though, I agree with this point of your post and I too would had liked for Larian to adjust the stats and enemies to avoid this issue.