Upgrading from Munificent Mogtome to Omnilex Zenith will give you a 5.58% flat overall healing increase. We all love crit, but it isn't consistent enough to negate the overall healing increase. Another thing to take into account is your groups Limit-break.

Limit-break damage works like so; it takes the overall weapon damage of the entire group and gives you a number, so by not getting either Omnilex Zenith, Cognitome or Direwolf Grimoire you're reducing your groups Limit-break.