Idk man, in a vacuum Mandi is definitely better, especially thanks to foul play, but I don't particularly like it because of toxic and knock off. Mandi more often then not will take one of them, or even both, or at the very least you have to be very careful about them, while corvi just doesn't care.I can't say I agree with your assessment about Kartana or Excadrill. Mandibuzz + Scarf Lando is an enormously better core for dealing with Kartana than Corviknight + Excadrill. Corviknight cannot switch in on an SD set, and if the Kartana is SD + Rillaboom (not an uncommon core), you lose at team preview. As for Excadrill, it certainly isn't a "toss up" between Excadrill and Landorus. Relying on 5-turn sand for speed control is a huge detriment in many situations, and worsens the offense matchup significantly. These aren't small issues, and they should definitely be considered when implementing improvements.
Definitely scarf Lando is more reliable than sand drill, but the Rillaboom+Kartana argument is kinda iffy (on paper still better with Lando+Mandi, that I absolutely agree with) because Lando without Superpower it's just tickling Kartana in grassy terrain and you can't intimidate-switch it because of beast boost potentially nullifying it.
The toss-up isn't about how to deal with Kartana or anything in particular, it's just about the choice of the ghost resist and what goes best with either choice. The Mandibuzz route leads me to scarf Lando + king + ferro but we use that core too much lol I wanted something different