Well, a few things about that. First, I would say under the old scoring for sure you'd be correct. But now...top position really isn't looked at as being all that important by the judges. If Khabib controls Ferg for a round on the mat but Ferg lands a few short elbows and opens up a cut on Khabib, it's the farthest thing from a certainty that Khabib gets that round under the new scoring.
And I honestly don't think it's a foregone conclusion Khabib just repeatedly secures top position. I mean, is it pretty likely he hits a TD or two early? Yeah, I suppose it is. He's obviously a dominant grappler. But he's never faced anyone who has the threat of locking up a choke from the front headlock position like Ferg (to be fair, I'm not sure there is anyone else that can do it like Ferg). Just the threat of that alone matters.
I'd rather bet the guy at +170 with a whole bunch of different paths to victory than the guy who's -200 who basically has one path to victory (albeit a very clear one that he's obviously extremely good at). And I think the skill and ability difference standing is more in Ferg's favor than the grappling difference is in Khabib's favor.