No, he's not. Probably one of the stupidest claims I've seen on HFBoards, and that includes Leaf fans claiming Matthews is better than McDavid.
I'm fine with having the discussion of who is better. And while I personally like Rantanen more, I can admit that it's Avs/Finnish bias and when you boil it down to a tee most people will probably lean on the side of Pasta. For me, Pastrnak and Rantanen are probably the closest pair to compare among star players in this league. Pick any two centers, any two wingers, any two defencemen, there will be a bigger gap between the two than with Pastrnak and Rantanen.
They are absolutely in the same tier of player. Rantanen should ask more than Pastrnak, because his deal is going to kick in two years later in a rising cap world. It's not really that difficult to comprehend.