It's a fairly loaded question in my opinion. Some fighters are incredibly good at one thing, like Ngannou or Khabib or Royce Gracie, some fighters have a much more varied skill set, like Jon Jones or Charlie Olives. In older UFCs the art of MMA was much less developed, and less money in it, so you probably had 'less skilled fighters' same like in most sports: the athletes of old had more limited skill sets than the latest gen athletes with top tier sports science, not to mention the latest gen has the benefit of learning from the trailblazers.
E.g. every man and his dog now is throwing front kicks, when Anderson Silva landed front kick KOd Vitor Belfort in 2011, I believe it's the first front kick KO in the UFC. Now it has become a standard technique.
A final point being, I have seen for quite a few years now people say heavyweight is a low skill division with a lot of overweight dudes who are just winging shots. In my opinion, being skilled = finishing your opponent in decisive fashion. Bigger dudes move differently to tiny dudes, and so even a dude like Black Beast swangin and bangin, is a skill in its own way, and I do not think that a bruiser who brute forces his way to become a champion, is any less skilled than a dude who employs a very wide range of techniques to outpoint his opponent.