That's debatable, shoehorning good players into the team is not a god idea.
He plays all across the front 2/3 behind the striker, fluid interchange which seems to be the go in a Koeman team.
Barkley, Kev, Calvert Lewin and Lookman e.t.c all move pretty fluidly in between those positions.
As to whether he's better than Kev, here's the stats in a team that finished below us last season and will do so again this season.
This season Kev averages an assist and a goal (4 of each) in every 370 minutes of PL football.
Siggy averages a goal (8) every 317 minutes, and an assist (11) every 228 minutes. Notably more productive.
Comparing last season Sigurdsson averaged a goal every 265 minutes (11) and an assist every 1458 minutes (2)
Mirallas averaged a goal every 250 minutes (4) and an assist every 500 minutes (2).
All that is telling me, as well as what I've seen of both players with my own eyes is that Siggurdsson is the better player, and younger at that too.