Loans often don't work for a lot of young players in terms of developing them for their parent club because they're simply not good enough. And likewise there are a lot of players who acknowledge the benefits and improvements that a loan spell has given them and helped their progress at their parent club.
The notion that a club outside the PL will actively ruin a player is a tad misguided as well. There are a lot of very good facilities outside the PL and well regarded coaches spread throughout the game who are all looking to impress and further their own careers. No benefits to ruining a young talent.
I'd agree there is no rush to send out a 17 year old on loan but if a player starts approaching 20 and has yet to show they're clearly capable of bridging that gap then a loan is often required, if only for the shop window effect, otherwise it clogs up the u23/u18 squads and having too many players around is detrimental to the quality of training.
...if this lad is as good as we hope, he won’t be going on loan anywhere because the Manager will want to use him. If he gets to 20 and we send him on loan, then I’d wager he won’t have a future here.