Innistrad is very well set up for low and mid tier play, without any Planar shenanigans. It has room for all the top-down horror themes and tropes, without any of the limitations on of Ravenloft.
What would be cool is a Red Masque of Death Victorian Steampunk setting book...
Almost every key element of Innistrad can be found in Ravenloft except Eldrazi and Angel worship, although Ravenloft does have Bluetspur, a domain whose Darklord is an Illithid Elder Brain.
Both planes have Werewolves check, Fiends check, ghosts check, Vampires check, flesh golems like things check, creepy constructs like dolls/gargoyles check, Evil Plants and Bugs check, monsterous elementals check, murderous insane humans check.
Innistrad Eldrazi monsters.
But Ravenloft has Doppelgangers, Illithids, Drow, Duergar, Death Knights, Liches, Mummies, Illithid Vampires, Demilich, Flame Skulls, Jackleweres, for example. And most importantly Darklords.
Darklord - 1d4chan
For Innistrad you really already have all the rules you need to play it except Eldrazi, it has almost no distinct monster types unlike other MtG settings, no unique playable races, no unique classes or subclasses thanks to Monster Hunter being released already, I mean you could basically just use the art book for Innistrad or the Planeshift article. Maybe you could use a few key NPC stats or an intro adventure. That is about it.
Ravenloft on the other hand has alot more unique rules and variety to it, it's a lot bigger and more diverse then Innistrad.