I disagree, I think LW has been completely lacking competent wrestlers for years, and with the addition of Islam and Dariush and Gregor and Chandler its finally better, but it used to be frankly pretty bad.
Kevin Lee was one of the only person's with high level takedowns, and he literally took everyone down that he tried. Tony absolutely does not have good defensive wrestling, neither did Barboza. I would argue Poirier's defensive wrestling is pretty bad for his level, a gassed Hooker took him down multiple times. Poirer's consists of jumping the gilly, and it shows a lack of fundamentals.
Gaethje's wrestling is pretty good, but his BJJ is non existent, and he himself has confirmed he doesn't train it. If Chandler or Oliveira or even Dariush got him down even once with more than a minute or two to work, he would be done.
Chandler has beaten people with much better takedown defense and grappling than Poirer or Gaethje have ever had. I don't see a problem in that department apart from Islam, because he would nuke Gregor's lack of striking defense, and I love Dariush, but he is too un-athletic to hang with Chandler.
I could go more into depth about my opinions into LW (or its former state) because honestly I have felt like the state of its grappling has been pretty shit in the top 10, and Khabib got lucky that LW had so few high level grapplers, because lets be honest, Conor, Gaethje, Poirer, Barboza, and Michael fucking Johnson are not cream of the crop grapplers, defensive or otherwise.
I get your point about size, but honestly he is so athletic he makes up for it. Hooker was in my opinion his toughest matchup in the top 10, and he showed that his striking is more than enough to make up for his height.