not so sure the dutch league would be preferable over an english league tbh. That wouldn't help in telling us if they could handle making the step up to our first team in the prem, i mean look at deulofeu, he'd look brilliant in the dutch league, but he's not good enough for the premier league, and that's not because he's not talented enough.
I agree with you about the Dutch League not saying anything about making it in the PL, but certainly with Dowell it's about just getting a chance to show that he has got that professional 'something' to give him that chance at the top level. Both of them have a queue of top-level players in front of them here as well as competition at their current age and level. Would you take Barkley out of the team for Dowell (the last match, OK, that's football)? Davies? Mirallas? Lookman and Calvert-Lewin are also seen to be deserving of the few chances that crop up for youth as a wide attacking/advanced midfield player.
With Walsh, you are talking about Gana, Davies (again), Schneiderlin, Barry, McCarthy and now Besic. Plus Joe Williams fighting for that spot. Plus potentially monkeying around with formations and finding spaces for Holgate, Kenny, Garbutt, Connolly and Galloway
You could argue that Deulofeu is a perfect example, since he was loaned out to England before he got his chances to 'make it' with Sevilla, us and now Milan. He didn't show enough to shove aside the competition at Barcelona so this was the solution found for him.