Theres not just one answer as to the point of a loan.
I think James has started as many games as he did:
1) due to his electric start. His goal on his debut vs Chelsea got him a start, then he scored a couple more which really helped him.
2) Lack of options. Hes not starting today if Cavani, Rashford and Sancho are available, because hes not ahead of them. So once two of them become available, he drops the order, big time.
Now based on that, I dont think James will lose his minutes to a kid, but to an actual option which is higher in the pecking order
So a loan would let him recoup the minutes.
A loan would also help him in terms of a different style of play and a different training hes not used to, which means he has to do more work to prove himself.
A loan would also help him with being more confident.
Keep in mind hes 23. There isnt a set criteria on why a loan occurs, but there could be a number of reasons, and one is to benefit the player long term. There also isnt a set age where a loan automatically means putting him in the window for other teams.