Ideally we'd have more ways to use all of our ressources (MP, Darkside and Blood) but that would require a deeper rework that we cannot expect for the 6.x patch cycle, and even less for release.
I wish we'd have a Dart Art style MP dump to augment some abilities (to generate another ressource or stuff), while Darkside could be spent to gain Blood, and Blood to gain MP or vice versa. Making the 3 Gauges communicating vessels of some sort.
Darkside being something we can spend would also discourage overcapping it.