Don't think we've seen the best of Feghouli and Nordtveit generally hasn't been played in his best position. Obviously Feghouli suffers because he basically plays in the Antonio position and Antonio is better but he showed when he was at Valencia that he is more than capable of decent performances. Similarly with Nordtveit at Monchengladbach. Why bring a player in, presumably because we've seen something we like, and then play him in a role he isn't accustomed to?
I'd basically keep both of them, unless of course we can bring in better. But imo we should only be looking to bring in players who can go straight into the side to improve it. Which would mean others dropping down into the fringe roles. If that happens then get rid but otherwise keep them on the books and let them do a job for us.
People who claim to be modest usually have a lot to be modest about.