This seems fair to me – for Koreans, the Hussar upgrade has a high cost to benefit ratio because of their lack of the other upgrades. Giving them Bloodlines would have balance implications for War Wagons though. Plate Barding and Blast Furnace would affect other units as well, of course, but not in such an impactful way.
Why? Do you think the free Bombard Tower upgrade is too powerful? Personally I don’t think it’s a problem, and think late-game towers in general are underpowered. It’s almost always better to spend the stone on a castle – especially if you have a good unique unit, which Koreans do.
Honestly, I don’t think bringing it closer to history is sufficient justification for such major changes to the unit – especially since this doesn’t seem very much closer to history to me. There really ought to be some gameplay justification as well. I also think changing the projectiles to arrows but having them no longer benefit from the fletching line is unintuitive.