I mean, based on the changes people have suggested right now, the Greyhound would be a four wheeled Stuart. What's the point?
People would still use the Canister Shot. It would still be useful, and it would still murder infantry, but it would squad wipe less and feel like a more consistent ability. Isn't that what most players want?
By buffing the Greyhound's base damage but reducing the RNG factor of its main ability you make the unit more desirable, and less rage-inducing to fight against. There is no reason that it can't act as a 3 CP doctrinal alternative variant to the Stuart for those occasions where you may choose to forego the Captain tier. Often doctrinal units are designed to fill holes in your standard tech tree, so why not?
Besides, the Stuart would still be a better unit by default.