I actually think rus horse archers are in a good place. They are squishy but with good range and decent price.
Mangudai on the other hand are pretty bad imo. You can build 2 archers in the same time with less resources. You can build a lancer for not a lot more resources which is way more useful.
Sure they can shoot while move but the low range kind makes this not as good as it should. Even raiding with them gets shut down so easily by a few units, walls or a tower. And then they just die incredibly fast.
They really need a buff especially after the next patch were springalds get nerfed and probably also the movespeed for infantry.
I made an in depth analysis about this a week ago if you want some details: