Hm, sorry if I misinterpreted your games history, it's rather confusing with all the resets. Anyways, I've come across several Minion Erebus players who deal insane damage, mainly because they also skilled Bite which lowered my already low armor and had 10 Nightcrawlers and 6 idol minions attacking me simultaneously. This strategy makes them unbeatable on Prison. The very few Minion Sednas I've encountered so far were not nearly as dangerous.
I've seen some 'guides' detailing a really cheesy minion build with Erebus, bordering on (or outright, whatever suits your fancy) exploiting since it takes advantage of the HoB bug. I haven't tried it, but could definitely see Erebus drawing a bigger advantage from these things than Sedna.