I gave up farming for Invincible’s Reins after many tries because I think it’s a myth and just doesn’t drop. But oddly enough I got some mounts with only few tries. Only killed Anzu for less than 10 times for Raven Lord. Even I got Ashes of Al’ar, don’t know how many times I tried for that one but somehow I got it.
I have a rogue alt which I don’t play much. I have both Warglaives of Azzinoth but it’s just a bank character sits on Orgrimmar and I login once or twice a week.
For Shadowlands open maps, I got all mounts and pets from rares except for the mount from Famu the Infinite. Some of them are just refusing to drop I guess.
I generally don’t farm mounts and the like actively - but do like to farm mats. Not longer than about 2 or 3 hours though, but if I know where to look for my mats and have a realistic chance at getting them, it can be a fun activity
So say, I enjoy farming high-end vanilla mats for mogs (retail) and for alt usage (classic).
Now, for a proper mount hunt? Maybe the Rivendare horse in Strat UD.