the main thing you want in a hero mount is strong capabilities you couldn't get otherwise. A mounted Dvar hero starts in a Bulwark, giving them access to Agile Overwatch (and Concussion Volley.) A Syndicate Psi-bike has an amazing main gun and AOE immobilize. But on the other hand, a Vanguard assault bike gives you little you couldnt get with a shotgun and a grenade. The good mounts are fine, its the bland mounts that feel pointless because they are.
The other problem is not intrinsic to Piloting but rather a matter of loot quality. You can expect to get at least some tier3 weapons over the course of a game with strong secondary effects, bouncing shots and so on. That does not happen for vehicle mounts though and even if it did you could very well lose the mount. Tier3-4 vehicle mounts are very rare as loot and not intrinsically stronger than research.