Considering he's been red hot recently, is it fair to say he's a top 3 centre?

One can certainly make the argument that he's a top 2 Center right now. If I were starting a team I'd still take Nate, but Matthews is definitely right there with Draisaitl 4th. I also think if the season ended today Matthews should win the Hart. And if he scores 50 he better win the Hart. That would be the most incredible season in decades, imo.

McDavid
MacKinnon
Draisaitl
Matthews

The best 4 centers in the game currently. Matthews at best is #3 while at worst he's #4

Yes, he's #3 in my opinion.

Him and Mack are close for #2.

This season he has definitely been the number two, only behind McDavid.

Overall I'd still say he's probably the 5th best C in the league, behind MacKinnon, McDavid, Crosby and Draisaitl.

Clearly top 4, although he, Draisaitl, and MacKinnon are neck-in-neck.