RDA fight with Khabib was 3.5 years ago. RDA wasn't a champ yet, hadn't gone on his huge championship run yet, and clearly still wasn't as good as he proved to be in his championship run. I don't put a whole lot of weight into that win anymore.
That, and Ferguson has a very different style of grappling than RDA. RDA is traditional in every sense, position before attack. It's part of the reason his top game is so absurdly efficient. It's also why he's, historically, been relatively defensive off of his back.
Ferguson is a lot more aggressive off of his back. The first round against Lee was really only dicey in the final moments of the round, but this "Lee almost finished him" is greatly exaggerated. Ferguson had made space and gotten out of trouble at the horn.
Frankly, what makes this fight hard to call is Khabib's inactivity. He's out for years at a time, shows up, beat some mid tier LW impressively (which we already know he can do), only to disappear for another year. Since RDA (again, which was three and a half years ago), he's fought twice. Once against a non ranked, short notice opponent, who people were a bit shocked he didn't man handle faster. The other against MJ, who has always been a fringe top 10 LW. He was at least fairly impressive in the latter outside of a couple early moments on the feet. But MJ has also struggled heavily with grapplers in the past.
I'm still not sold on Khabib. I'll hold any further opinions on his ability until after his fight with Barboza.