Oddly enough, though I'm huge fan of nuance and highly context-impacted calculations that may invert a typically-held guideline, I never really feel all that thrilled by fail states like these, especially when the player impact of the mechanics seems at odds with the job theme in that state. Being overwhelmed by one's Voidsent = be careful not to overspend? ???
In a game with greater technical/coding competence, rather than having Communio spend stacks and copying old Req-Confiteor's fail condition (I consider PLD to seem far more deliberate/methodical than a Voidscent-enraptured scythe-man on a killing spree), I'd prefer it if each spender raises the damage of the next Communio but that bonus fades, by percent, over time, so that instead of that mechanic feeling "measured" and strictly timed, it instead feels more opportunistic and capitalizing... more predatory/cruel... in that it may want to pop it slightly early after a string of crits, or gamble that the string will continue (for even bigger blasts).
Agreed, though, that SMN lacks that sense of pivotal moments or "destinations" or the like. I feel like part of that, though, is just inherent in the summons' being phase-starters instead of feeling at all like rewards or capitalizations.
:: Food for thought: What probably kills small, highly-nuanced optimizations the most... is just the super obvious/unchanging win/fail conditions that tend to heavily punish "mistakes" more so than "errors". A lot of the times a low floor and high ceiling aren't just paired design goals, but a high ceiling almost seems to inadvertently cause things that in turn cause an accessible floor.