Have some patience, first he wasn't hitting enough now it is his fielding. Players do not come up as finished products. They need to learn what it takes to be successful in the major leagues.
Luke has started 161 games from college tot he pros at 2B, maybe he doesn't improve, but that is just a year of starts. Can he improve, I don't know but he is athletic and appears to have the work ethic. Give him some time, Koskie was a butcher at 3B when he first came up and he became a good third baseman. We always want immediate success but it doesn't always happen.
As for hitting for power, sometimes that comes with experience, have heard many former major leaguers make this point.
All this said if you have a better option, then move him or move on. But we don't have a better option and no Kriedler or Gray or other AAAA types are not the answer either. Either bring someone in that can, that actually has and can play the position and has shown they can be a starter at this level or stay with Luke. We have to start defining these positions and stop moving everyone around. Keep Clemens as the super utility player, he is one who is comfortable moving around and play passable defense at multiple positions.
The team needs to decide what players they have that they can count on for roles going forward and where are the holes are and make the moves to fill them. Unfortunately with no real leadership in the front office, I don't know when this will happen. And we will just keep floundering around .500 and tease us enough to pull us in and then have a stretch of games where they look like little leaguers out there.