Should Unsynced content give rewards?

[Vazoth]

I realize that's what you'd like to think your point is, because you think it makes your argument sound less petty. But what you're really trying to argue is that people shouldn't be able to get a pony in a way that's easier than the way you got it because it makes you feel less special...

The OP might have some personal feelings here, but first and foremost it makes the mounts less special in general.
Achievements and progress are two different things. It shouldn't be about walking a certain distance, rather than treading a specific route. I don't see, why everyone should be entitled to own the ponies, if they aren't able to meet the requirements.
Please notice that I myself don't have any of the ponies yet and still, I completely take the OP's side on this matter.

...All you're doing is making runs like these even longer for OUTDATED rewards...

I'd only call rewards outdated, if they get replaced by future content. In case of the primal mounts, this is clearly not the case. Therefore, they aren't any less valuable now, than when they were first introduced. Just the demand for them declined.