Van Dijk has been elevated to absurd levels of praise because the level of defending other than him is generally quite poor right now. He's obviously a very good player but he doesn't need to do as much to stand out as people like Rio/Terry/Vidic did, not only in the PL but on a global level.
In the peak of Vidic/Rio/Terry etc, pretty much every club in the top sides had a very good defender. Liverpool had people like Carragher/Hypia, Chelsea with Terry/Carvalho, Arsenal with Toure/Gallas, Tottenham had people like King/Dawson etc. Now I'm not saying that the level of that selection is World Class but it's a much better spread than we see now.
Why Van Dijk is mentioned on this thread? He’s on the list no doubt but definitely still below Campbell, Vidic, Rio & Terry. What Van Dijk showed this season and last season is something that the others already showed since 25 or 26. He needed 2 or 3 years later to finally start catching the greatest.
Vidic was absolutely brilliant for the first half of 08/09, the best half a season out of any of them, but he fell away quite a bit in the second half of the season (by the standards we're talking about here).
I'll be honest I was fairly young for Pallister so don''t remember him much. I would say he was during a period when the English game was significantly below the other top leagues though (both in general and his position specifically), whereas the others all came when we were competing with the best in europe.
Personally I rate VVD last season as better than any of the others you mentioned (other than Rio 07/08). As much as I hate to say it.
You can basically have two separate discussions about it. Is his level the last two years amongst the level of the greatest defenders ever in the PL? Most definitely. Is he in the conversation for "greatest PL defender ever"? Not yet, you don't deserve that after just a few years imo, but it's also useless to talk about it right now when he still has years left at the highest level. Would make much more sense to have this discussion if he goes back to the Netherlands at 34 for example.
Same goes for Ronaldo. He is the greatest player to ever play in the PL, but he's not the "greatest PL player ever" because he didn't stay long enough for me.
Rio has more sense than Kompany. He said he thinks VVD is quality but he would like to see how he would of coped playing against 2 strikers every week like he did in his day. Now its one which is easier to handle.