I say this as having only played RMD on Frontlines (don't play Feast), but my biggest gripe with RDM is illustrated below:

You start by casting your Ver spells to build up white/black, you then use Manafiction to get up to the 90s-100. You dive in, try your melee combo which is actually quite annoying given that people often sprint away (and you may not have spring up at the moment). When you finally land your final melee hit, the target is dead. You get excited you can now use Verholy or Verflare. However, you look around and there is no one in sight. Or, the enemies you do see are so far away and you sigh in frustration as you realize you aren't going to be able to use Verholy/Verflare because it falls off so quickly. BLM and SMN get access to their big move indefinitely (until they use it) but after all that work RMD loses theirs after 5 seconds.