Thanks for your insight. A point about soul capacitor overkill: there were several reputable independent sources stating plausibly that critter/low lvl mob damage could be harnessed by SC in timwalking dungeons and repurposed holiday dungeons. I've been able to get weird legacy damage buff effects in arathi basin also. That said, these legacy buff effects do not seem to work in higher lvl areas like draenor and, as you say hfc.
So I basically agree, but technically it seems that soul capacitor damage does something a bit more complicated than simply ignore overkill.