Did you seriously mention Gaethje as one of the better grapplers Khabib fought? Poirier is a noticeably better grappler than Gaethje, and for all the flack his grappling gets, McGregor is a clearly better grappler than Gaethje as well.
The best overall grappler Khabib fought was Ali Bagov, who was one of the best grapplers in MMA during his prime in the mid-2010s, but they fought before either were in their prime. Bagov, especially, was far behind the level he'd get to years later. It was still clearly Khabib's best pre-UFC win, and a better win than a number of his UFC wins. Even though he wasn't in his prime (and his fight with Khabib was at WW), Bagov submitted Emeev in 1:30 at WW in both of their 2nd pro fights, and that remains the only submission loss of Emeev's career 16 years later.
I would say the best grapplers Khabib fought were:
Bagov
Tibau
RDA
Healy
Tavares
But Bagov wasn't in his prime, and many thought he lost to Tibau. After those 5, it's probably guys like Poirier, Eldarov, and Shalorus. I don't think the vast majority of his resume past those 8 are notable grapplers.