I'm largely going to skip the thesis of this. UVs are wildly expensive money sinks that no one really enjoys putting up with. They are a massive bottleneck for armor design and need to be changed before armors have any hope of really improving.

I'll start with the application of UVs to armors: There will no longer be "Low, Med, High" and so on, or at least not in the traditional way. Each UV is just a one point instance of that buff and you can get multiple of the same UV on the same armor. Armors can have STATIC UV slots that you can put UVs on. This adds another outlet for balancing armors! On top of defense values and innate UV bonuses, we can raise or lower the amount of UVs an armor is allowed to have applied based on how powerful the devs think the armor already is. As for how powerful each UV instance will be, that's a little hard to dictate as things are now. I'd start with something between our current low and medium and go from there. Having more than one instance of a UV will start raising its total from Low to Medium and so on.

We also need more types of bonuses. Our current selection is cripplingly small. Counter to what I literally just said, I think we should get rid of monster family damage bonuses. They are far too situational to ever really be worth slotting in. I get more out of stacking ASI or CTR than just doing more damage to slimes per hit. ASI and CTR are fine to stay, but how about we add some more mechanically interesting stuff? Some armor exclusive UVs could be more widely build affecting while weapon UVs would probably want to only affect the weapon. Additionally, keep in mind we don't need to design every new UV to stack up to 6 points. If a UV would work best as only going up to 2 or 3, then that's fine. Just make sure that the game communicates to the player when they've hit the maximum as well as what amount of points it took to reach it.

Completely remove any RNG involved with UV acquisition. This isn't even just because I think gambling for UVs is bad, but rather every time we add a new UV type it further dilutes the pool of UVs we have to gamble in and just makes it impossible to really improve the system without making something worse in the process. If enough UVs are added, we can still retain the money sink aspect just from how many different UVs people would want to try out.

Here are some ideas for armor UVs:

Battle Sprite Cooldown Rate: Pretty self explanatory. Very simple idea, and maybe we could have other UVs to affect sprite abilities in general. Preferably none should only affect a specific sprite though or you kind of have the "Family Damage Bonus" issue again. Not that UVs can't have a tailor made effect for a specific sprite's ability, but rather if it affects one sprite it should have other tailor-made bonuses for the other sprites without needing a whole different UV for each sprite.

Adrenaline: Up to 3 points. Short movement and attack speed boost after a charge attack. Duration scales with points invested.

Evasion Mastery: Up to 2 points. If the knight's dodge i-frames touch an attack that would've dealt damage, cut the dodge cooldown by 1/3 for 1 point and 1/2 for 2 points.

Here's some ideas for shield UVs:

Parry: Up to 3 points. If the player activates their shield just as an attack would hit, reduce the shield damage by 1/2 for 1 point, full negation at 2 points, and stun the attacker on parry at 3 points. If the attack is strong enough, ignore SOME of the bonus. e.g: Knight has 2 points on an average 5* shield and parries a Trojan slam so only negate 1/2 of the damage or none on 1 point. If the player is using a lower star shield than the area probably demands then make it much less likely to negate anything. Note that due to the nature of playing online, the timing of parries would probably have to be a little generous to account for lag. Probably needs to be tested a lot to find the best middleground.

Bulldozer: Up to 2 points. +50% distance on shield bash and dramatic bash damage boost and 50% damage reduction on 1 point. +100% distance on bash, aforementioned bash damage boost, can control trajectory mid-bash by changing where the knight is facing (can make curved paths), and can shield cancel the bash (the distance will be very long by this point so cancelling would be desirable), as well as one-time 100% damage negation and any following hits are only a 50% negation at 2 points.
Also to make this not incredibly janky, I think enemies knocked back by the bash even without Bulldozer investment should knock back other enemies they collide with to ensure that a shield bash won't be stopped by enemies getting pushed together too hard. The idea behind this bonus is to clear paths rather than really deal damage so it'd be a shame if the path was stopped because of janky knockback behavior.

I know these bonuses are much, MUCH more complicated than the stuff we have now. Very far out there ideas, but that's the point. UVs in their current state are incredibly simple and I don't think we can really get anything interesting done by sticking to such tight limitations. My ideas obviously aren't the only way to go here, but I really don't think anything short of a complete rework of the whole system will be enough. As I've said before, UVs suffer from both a small pool of worthwhile bonuses to choose from and having to gamble to get them in the first place. If we add more UVs to play with, we further dilute the pool and make it harder to get anything one would want. If we remove RNG, then we're still left with a boring system. UVs need a lot of work to be fixed.

I'm really just having fun here writing UV ideas with no expectation of them actually being added but the main takeaway I want people to get from this post are my points about the point system to add new avenues for balancing armors and weapons, UV variety, and RNG removal.