After constantly testing, I can pretty much confirm that heating Shields AND adding non-status UVs are completely pointless and is actually pretty redundant.
It seems that unlike Armor and Weapons, Shields do not make much a difference from a single bar:
Each Tick on a Shield's bar is equal to about 2% resistance to that damage-type. Meaning that a Dragon Scale Shield will only make a 14% difference against Piercing and Elemental attacks. If an enemy is inflicting double (IE: Piercing and Elemental in this case) the damage absorbed would be 28%.
As for UVs, each UV rank is adds about 1% to the absorbed damage:
Low UV: +1% (+0.5 Bars)
Med UV: +2% (+1.0 Bar)
High UV: +3% (+1.5 Bars)
Max UV: +4% (+2 Bars)
Each Tick on the Shield: 2% (IE: Med-High UV)
When heating a Shield from Lv1-Lv10 (this is 5*), you will actually only gain a 1.5%-2% increase in resistance for each bar present. Every two levels gives you .33% resistance to each bar that it has. Meaning an Aegis will gain +1.5% Resistance to Normal and Piercing Damage, a Dread Skelly Shield will gain +1.5% to Normal and Shadow damage, and the list goes on.
Each enemy seems to have a base damage of inflicting damage and that sets the amount the Shield can resist. A Wolver on Elite deals 50% Piercing damage to a shield without Piercing Defense. With Piercing Medium, that amount is increase by about +2% and so on.
In fact, just for the kicks of it, I decided to try numbers with a Wolver and took a prediction on them for how much damage they would do: I was nearly spot on, I was about 1% off of the target. I guessed that Dragon Scale Shield would survive with 63%, it was 62%. Royal Jelly Shield was 65%, it was 66%.
Something rather interesting though is that unlike Knights, Shields can gain immunity to all forms of Status, be it Weak, Moderate, or Strong. Zeddy confirmed that a Slag Walker's Breath inflicts Strong Fire. Dragon Scale Shield despite not having any Normal OR Shadow resistance, was immune to it. Something rather interesting about this is that Status plays a huge role in how much damage a Shield takes. It's pre-set by OOO and can inflict anywhere from 20% to 40%, this is equal to about +10 Bars of a single defense - +20 Bars of a single defense. Enemies have two types of attacks: The base attack and the Status attack. If a shield has immunity (IE: Crest of Almire has immunity to Shock and Fire) against that status, it will not see the second variable of attack.
The major problem here is that this applies to all difficulties, you will still see 2% resistance for each bar on the Shield. However, damage is increased overall by +3% per damage-type on Elite, and decreased by -3% per damage-type on Normal. The base being about 6%.
This means that:
-The reason that Volcanic Plate Shield can survive Vanaduke's attack so well is because Status isn't being inflicted on the Shield and Elemental resistance would only make a trivial difference.
-Omega Shell can only survive the attack because of the HP boost, from data I believe the increase is about 20%, allowing it to barely survive an attack from the mace.
-Status really DOES outweigh defense, to compare, a double Max UV would only provide an 8% protection. Where-as a maximum status will protect you from the second variable which is over 20% damage and so far can be up to 38%.
-Heating a Shield is completely redundant, the only reason to actually heat it is the chance of Forge Prize Boxes or to access higher-tiered rank: HP outweighs both Status and Defense.
So aside from this, I'm thinking that Shields need some sort of buff. The fact that heating only provide a 2% difference is absolutely horrible.
We've been discussion your study in detail in the Wiki Editors forum, so I don't have much to say here, except: Thanks. This is very interesting and good to know.