Afaik horn and tatar are both composite bows while the longbow is a one material bow made out of a material (wood) that has a rather low maximum spring speed. That means even with decreasing the arrow weight the longbow would hit an upper limit for projectile speed, which is around 60 m/s iirc. A composite bow circumvents that problem with using a high spring speed material in combination with the slower wood. Steel, as used in high powered crossbow, has a high maximum speed as well.
So yes, one has to imagine in cRPG that the longbow uses different, heavier arrows than other bows. But that is what happens in reality anyway. Also Tydeus did it.
I'm sorry but from realism point of view it doesn't make sense.
If same arrow is shot, what defines it's damage? Speed.
If you want different arrow weights, implement them, so for e.g. arrows with higher weight (and damage) are much more accurate with Rus/Long Bow, arrows with lower weight have chance to break or less accuracy with higher difficulty. This won't happen anyway though.
So having less damage and higher missile speed is not realistic.
In reality Long Bows were long range weapon with low close combat capacity, as it was always in cRPG.
Now from balance point of view.
Firstly, "insert random rage quote about changing missile speeds for archery", and I agree with those... mostly. It worsens players accuracy much more than "accuracy stat"
Secondly, Long bow was always a sniper bow, with it's speed and damage. Now it's not effective at all.
I've always used it not because of damage. but because of missile speed.
Actually after that update I didn't even look at it's stats, I just stopped using it because it didn't feel right and any good to use.
My archers are alts to clarify
EDIT:
I've looked at bow missile speed stats...
It has no sense to give higher tier bows lower missile speed - it is the best stat for bows.
At the moment you are able to have pin-point accuracy with tatart bows and even deal a lot of damage. Yes, more damage than Long Bow in capacity of hitting more targets close, much more targets at longer distances. And damage stat suddenly becomes useless.
How it should be by missile speed stat:
Short bow - 40
Nomad bow - 42
Tatar bow - 44
Bow - 42
Horn Bow - 44
Yumi - 38 (ultimate HA weapon with it's accuracy and damage)
Rus Bow - 42
Long Bow - 43