I had a similar idea that Lethys1 had when I noticed the same problems. It might work, but I think we should look at the root of the problem.
The problem arises because the game is pretending to be an action-rpg without any real action-rpg mechanics that work. With no defense stat, that rogues usually had in good supply, getting hit means you are hit and take damage. That's pretty bad for a class that has no guard and no con bonuses. This game handles and feels less responsive than DA2, and that game wasn't even an action rpg (despite popular disinformation).
To avoid taking damage, you need to physical move out of the way. The game expects you to spend spend talents and a skill slot just to be able to do that. And even then, because of sluggish movement, being stuck in animations, collision detection, and no invincibility frames on evade, you most likely end up getting hit anyway. Can you imagine if Dark Souls expected you to spend 5 levels in dexterity before you can dodge? Or Skyrim asked you to spend 3 talents to be able to block?
With regular enemies, this isn't much of an issue, because with good enough gear a party of 4 can kill them pretty quickly even on Nightmare and between stun/knockdown on so many abilities, regular enemies spend a great deal time CC'd.
On bosses and CC immune large enemies this doesn't work. Worse, even correct positioning doesn't work, whether to design or bugs I don't know, because of 360 melee aoes (which also punishes with playing more than 1 melee in general). The only fesabile way to deal with them is war of potion attrition, 1 shield tank + 3 ranged, or proper management of multiple barriers.
The funny part is designers were at least partially aware of these inherent imbalances in the system. Someone during the development realized that these action mechanics barely work and melee just ends up relaying on health potions to stay in the fight. Damage is essentially unavoidable. So aside from giving so many abilities cc properties to stop regular enemies from doing too much damage, I suspect they added Guard and Barrier, 2 passive numerical defenses in an game trying to be an action rpg, to offset this. Rather than having workable action mechanics, or passive defenses stats that opposes attack values like in the past two games, we have abilities that exist solely to take unavoidable hits. I'm not an expert, but that sounds like a pretty bad recipe for an "action" rpg. I mean, that is a system or resource management and not an action rpg. Like the last two games actually, except with less tactics and choices and even more imbalances.
On a side note, on higher difficulties, guard is borderline worthless. It seems to roughly scale as 25% of your max health, and the 25% extra guard passive does not work. On Nightmare, 200 extra hit points usually won't last longer than 1 or 2 hits. And that's with a full guard bar, which isn't always easy to get. For Guard to be useful, you need armor that mitigates so much damage that Guard becomes a moot point. Guard needs to provide significantly more hp to be worthwhile in its current form. Like Barrier, which provides so much extra hp that it's pretty much invulnerability. Ironically enough, most powerful attacks are best dealt with a properly timed Barriers in order to mitigate the damage and not Guard or dodging. Shield Wall works too, which is why best partly comp for bosses/cc immune enemies is simply a shield warrior + 3 ranged.