Honestly speaking... no
Something that I saw pointed in random youtube videos a few days ago, with Champions coming out, Mythicals will not be locked out by "being there for events" anymore. Most likely you'll be able to "buy" any pokemon with enough grinding just by playing.
This means, Myths may at some point be part of official formats. They've been tackling with it on "non-relevant" seasons so far, but with Champions coming, it's not completely impossible that we eventually get official score-valid formats with Mythical mons allowed. And we want nothing of unnerfed Dark Void there.
I meant only in reference to singles, but hey either way.