Probably an ideal move for him. Arsenal don't look interested in playing him after all.
seeing as the gunners are in the hunt for multiple pieces of silverware.
And frankly we're cocking up the prem.
I was neutral on Zelalem's move to Rangers last year. Sure, he got playing time, but the competition in the second level in Scotland was just terrible. Rangers are a decent enough club historically, and they're probably on their way back to that level shortly, but their relegation a few years back really hurt their status as a feeder to the top leagues in Europe. I think he could have gotten just as much playing time against much better competition.
Now that Rangers are back in the top flight of Scotland, at least their competition will be comparable to some of the European second divisions. That seems like a good level for Hyndman to spend a year or so. At his age, after spending five years in Fulham's system, he needs nothing more than game time against decent competition. Rangers are in no danger of relegation, so I imagine he'll get plenty of chances. He wasn't getting any time at Bournemouth, and he's probably not up to the Premier League standard. A bit more seasoning might bring him up to that level. Sitting on the bench at his age almost certainly won't.
Hyndman could have gone to Celtic this past summer but wanted to try and play in the EPL. Perhaps he'll get back, but he absolutely needs first team playing time to get there.
Zelalem to BVD is a good move for the reasons you note.