Best ring set after unlimited?

Couldn't you say that the Ark rings are beneficial as well since they give out potential or is it not 3rd tier?

They're first tier, so they're not as good, especially with things like MEEs, whose bonuses, like with potential, are based on level.

It kinda makes me sad that the level of equips matters so much, I mean, higher leveled equips should be better than lower leveled ones, but, there isn't that big of a difference between the items, all equips, I mean, themselves, regardless of level, I mean the first ~110 levels worth of normal equips don't even give you double digit stat boosts, and hell, even some low level stuff is better than some high leveled stuff. The biggest difference comes from potential and MEEs, and other things like them, like, cash based stuff.