@MountainDrew What exactly are you trying to accomplish with these limits anyways? Life regen and damage reduction caps only affect players who actually get hit. For a player who is able to dodge things very consistently, no amount of limits on DR or life regen is going to do anything to them. To this point, I've never actually experienced an amount of DR or life regen that I would classify as making me invincible. For reference, I pretty much only exclusively use Calamity and Fargo's in terms of content mods, and I have never actually crafted the end game soul items from Fargo's.
Kefke alluded to something that seems troubling to me. Are you actually balancing Calamity around other mods? If you do so, you're hurting the players that don't use said mods. As Kefke said, there is nothing you can do about players who want to play in god mode.
Also, the *reason* vanilla Terraria doesn't have limits on these things that you call broken game mechanics is because it is actually impossible to reach these "invincibility" levels in the vanilla game, at least from my experience. Players have obviously created ways to mimic invincibility (slime invincibility, etc.), but these have nothing to do with DR, life regen, etc. If these things are causing problems for you, it is because you added items to the game that caused the problem.