Let's be clear different managers take different views on players. This cliche about managers seeing players every day so they know best is total bollocks. There's countless examples of players stuck in reserves & then a new manager comes along and they are in the team and doing well. If Koeman was really concerned about Dowell's development he'd have sent him on loan last season.I dont care what he thinks.
Personally I've got little confidence that Koeman will give Dowell a chance next season so I'm glad he's gone on loan. It's a waste though.