MightyZehir
Explorer
WotC has indicated they plan to be pretty sparing with functional errata in 5E. Mearls has been quite forthcoming when the issue is a rule that needs clarification, but this isn't such a case; it's clear what the spell does. It's just that what it does is wreck legendary creatures. Even if WotC does ultimately decide this spell has enough issues to require an official patch, the patch is unlikely to come via Mearls's Twitter feed.
Yeah, the spell would be fine if it doesn't include slimy doom. The stunned condition is what destroys an encounter and it gets far worse when it requires 3 saves to end it and legendary resistance doesn't even help much.