Matic is transferring from one premier league rival to another top side. He has been heavily involved in two title winning teams in the last three seasons. And he is going to most likely cost less than Sigurdsson, and is only one year older. Completely different pedigree.
He's a year older, he's going to cost 40M, he's also a defensive middy. If we needed one, heck, if we didn't have Klassen, sure he'd be great.
And that's wonderful that he won two titles, but that doesn't make him a better player than Sigurdsson. I would argue that Gyfil keeping Swans up last year was every bit as impressive as Matic's contributions last year to the title.