I don't think it's fair to judge a player simply by his appearance count. Sigurdsson wasn't even being played by Hofenheim before Rodgers brought him to Swansea, and he's quite clearly good enough.
Though I do understand your point. Certainly, being given a starting place on multiple occasions for the world's very best team is a good sign. And despite the fact that he relies on his speed to do his work, I don't think it's necessarily too bad a quality considering we don't have any players that are real speed merchants, and it's good to have one of them around for sure.
Theyre very different players though, regardless and I wouldn't view them as an either/or trade off. I'd love either Holtby or Tello in a Liverpool shirt.