In short, my idea is to allow heavy armor to move a little faster.
The reasons why I feel this way is because I feel like kiting is a significant source of damage reduction that heavy armor players do not have access to (their relative speed being slower than many opponents and even some while sprinting). While invincibility frames are also a very significant damage reduction, they are not as helpful when you are being attacked by multiple targets. Running can be helpful in those circumstances, but costs stamina (which if you are playing a tank will be in low supply, especially while running). Thus, I feel like heavy armor makes you take a lot more hits, but also from a lot more enemies, and more enemy types (some being faster than others). I do not have any data, but I feel like the extra damage you take as a heavy armor player is greater than the larger damage reduction it gives you.
Therefore, I think heavy armor slows players a little too much. Removing this completely would render light armor worthless, and raising heavy armor's armor value would also (and possibly be overpowered). Thus, my thought would be to add a skill (perhaps called "March") that can remove up to half of the slow from your equipment. 1. This would require work to level up/not lose. 2. This would not remove the balancing slow completely, or increase the armor value. 3. it would make walking more viable, (which is slowed by armor, and does not increase with the run skill), so you dont have to sprint as much. 4. This would also lessen the reliance of heavy armor players on having Eikthir active / putting weapons away in combat when they need to move. Perhaps it could get XP by any walking with a slow effect active, perhaps proportional to the slow that is active (so the full 35% reduction levels up faster than only 5% from a single spear). This way, the skill would only really level up on tanky players who need the benefit.
The main hope for this idea would be a Quality Of Life for players who want to play a full tank especially for multiplayer, although this would help make heavy armor more viable for solo as well.