Pretty much any player who isn't a superstar at the top of the draft (McDavid, Matthews, Eichel, etc) has a floor of being a non-NHLer or fringe 4th liner/bottom pair unless they have dramatically improved their stock post draft. Just look at guys like Filatov, Cam Barker, Scott Glennie, Zach Hamil, Picard, Valabik, Yakupov, and Griffin Reinhart. Then there are a bunch of guys who carved out careers but are mostly back-up goalies, bottom pairing defenders or bottom 6 (closer to outright 4th line guys) like Hickey, Brule, Skille, Brian Lee, Luke Schenn, James Sheppard, Jared Cowen, MPS, Gudbranson, Brett Connolly, Burmistrov, and McIlraith.
It'd be insane to suggest Sergachev's floor is a top pairing defender. His game has so much risk, he could end up being a guy who never makes the league. That isn't a likely outcome, but it is his floor. Realistically, he should be able to carve out a career as a top 4 defender who has the potential to be a franchise defender. Cal Foote's foot speed could easily see him end up like a Jared Cowen who just doesn't have the speed to keep up at the NHL level. I think he makes it, but his floor is a minor league player.
The odds of getting a top 6, or top 4 defender where you drafted Foote is around 40%. So logically, a guy drafted in that range is far from 100% to be a top 4 defender.