Defense rings (tiered) are kinda bad. The only thing that is worse is a VIT ring. I know its unnecessary since everyone pretty much agrees that HP is better than DEF but i thought it’d be fun to do some simple mathematics around it.
In order to calculate the effectiveness of, lets say, a UBHP vs a UBDEF, lets use this equation.
N = Dn
Let N be net HP, D is damage prevented and n be number of hits. To input the rings this means:
UBDEF: N = 9n
UBHP: N = 180 (in this case n = 1 since a UBHP will always prevent 180 damage.)
That essentially means you need to be hit 20 times with the UBDEF ring just to net gain the same amount of HP as the UBHP. Okay but what if your HP is below the +180 a UBHP gives you? pretty useless if you are always below that margin, however you need to take into account the situation that got you into that in the first place. for this we’ll use the proportions of the Player’s health as i feel it is a better representation of how to look at this argument.
Let’s take a knights base max HP of 770, with 0 defense and faced with an attack, lets call it white flame, that does 280 damage. lets create an equation that can see how much percentage each ring can give you in terms of this knight’s health and compare it to the damage. It will incorporate the last equation.
UBDEF = (9n/770) x 100 = 1.16n%
UBHP = (180/770) x 100 = 23.4%
So a UBHP will give you 123.4% HP while the UBDEF will give you 100% + 1.16n% but in this case n would be 1 since the attack is a single white flame so essentially it gives you only a +1.16% in HP. But maybe we’re being too harsh on the UBDEF so lets split up that 280 damage into 28 pellets of 10 damage.
UBDEF = 1.16(28) = 32.48%
UBHP = (180/770) x 100 = 23.4%
In this case, with the UBDEF you gain a +32.48% in HP. Seems like a pretty good improvement however if we consider proportions in relation to the attack its not so impressive.
UBDEF = 280/(770(1.3248)) = 27.4%
UBHP = 280/(770(1.234)) = 29.5%
We can see that there is only a 2.1% difference in proportion. So after the attack you’ll be left with 72.6% of your “HP” with a UBDEF while having a 70.5% with a UBHP. However its worth noting that this is in proportions of their respective hypothetical HP buff, in reality there is about a 10% difference in HP (UBDEF: 752HP vs UBHP: 670HP out of 770HP) after the attack but regardless puts into perspective that the UBDEF will only be a little bit more effective even in a generous situation which is unlikely with late game enemies and bosses dishing out hundreds of damage at a time.
(If you’re wondering about a pyra, it is +(13 + 0.5n)% with a net HP of 100 + 4n meaning you’ll have to get hit at least 20 times to cut even with a UBHP, same as the UBDEF oddly enough.)
However if the nature of defense rings is to net HP by taking damage, than it ultimately makes it less efficient than any HP ring. The only way i can see having more defense as better is if it is an absurd amount of it (like the knight or a jugg) but since a UBDEF ring provides such an underwhelming amount HP rings are ultimately superior, paramount, exalted or even unbound.
TL:DR - Defense Rings Suck. Use (net HP) = (DEF) x (Amount of Attacks)