I would honestly remove Siege and possibly Capped Ram from the Huns’ tech tree. Of course, I’d give them Siege Onager and maybe Heavy Scorpion as a compromise.
The way I see it, is that Tarkans are essentially mounted Rams that exchange infinite pierce armour & DPS vs buildings for speed & the ability to fight units. Sure, you can mass up both just as easily thanks to Marauders, but would you really use Tarkans when you have Rams that can do the job just as well? In my experience, the only reason I would make Tarkans in the first place is if I needed to move my anti-building from point A to B to C in record time. Their pierce armour is nice, but if I wanted to take down archers, then I’ve got Paladins for that.