We literally get no power from the Dragonriding system. Try again.
The issue players have with borrowed power systems is when we as players get more powerful (be it because we get awesome weapons, abilities or traits) and then at the start of the next expansion that ‘power’ is removed because it was only valid for that expansion. No one considers the Garrison to be a ‘borrowed power system’ or the class hall in Legion, because even though neither of those things continued into the next expansion, none of them granted player power, so losing them wasn’t a big deal.
On the other hand players really cared about losing their artifacts in legion, having their legion legendaries no longer function at all, losing the heart of azeroth, azerite powers and corruptions from BFA etc. And they’re going to feel the same about losing access to certain covenant abilities (not all of which are carrying forward into Dragonflight) and bonuses given by conduits.
You know what they’re not going to care about losing? Covenant halls and the associated activities tied to each one (such as the Winter Queen’s Conservatory and the Fleshcrafting Workshop), because that’s a Shadowlands system that isn’t carrying forward into Dragonflight, but it gives absolutely no player power.
Now if Dragonriding gave everyone a sweet dragon flame breath ability that could be used in combat, that would be different. Then Dragonriding would be providing player power, and it would be considered a borrowed power system.