On the same token, players come here from Barcelona, Real Madrid... not exactly slouches when comparing them to your Wigans, your Birminghams, your Prestons... and meanwhile, we send one of our own players to the Championship, he impresses, and what do you know, he's able to play at a decent PL level.
I don't think any of us has said that Spence is on the same level as Skipp or that he's undoubtedly ready to be our RWB starter for the rest of the season. On the flipside, this is a player that's supposed to be developing so as others have mentioned, that process could be slightly painful as he beds in (if he's deemed to be good enough) but should pay off sooner rather than later. I don't see any pay-off coming with Royal or Doherty.
And as for Royal, I think his defending is quite overrated here. He's not bad at defending by any means, but he's not excellent or great or fantastic. It's also not like anyone wants Royal or Doherty to be awful so Spence can play; imagine if we didn't have to worry about the RWB position.
The fact of the matter though, is that if Spence isn't good enough either in terms of potential, then we need to stop wasting time and get a real player in there.