I can understand people thinking he's unlikely to displace Rooney and RVP, but why anyone would want him to leave the club is beyond me. If anyone thinks we'll get a better 3rd/4th choice striker if he leaves, they are very much mistaken.
He's been good when he's been given opportunities up front this season, and has been pretty clinical. He'll really benefit from, hopefully, getting some decent service from the midfield next season. Not all 23 year old strikers are the finished article, the lack of patience for a player who has come through the academy and has regularly been played out of position is quite astounding.
Consider Drogba at 23 years of age, he was playing in the French league, scoring and playing less than Danny. Not saying Welbeck will go on to be as good, but the raw materials are definitely there. His finishing is something that can definitely be improved, we know he's capable, he just needs to start doing it consistently. He won't do that unless he gets a run in the team when his performances merit it though.