Yes you're right. Long bow is balanced in that way that no one uses it today. This is a topic for discuss if longbow is balanced compared to the another bows, and now, it isn't. So there are two ways to fix it. Nerfing all the bows or buffing Long bow. Why all the archers are using horn bow? Why only few archers use Rus Bow? Why no one use Long Bow? The top-tier bow need to have something that invite players to use it. Now it's useless. +3 Dmg for -8 speed is a SCAM.
No, I think I just covered why the bow is balanced. Balanced does not mean equally practical. Longbows aren't practical bows, they're specialized bows. Rus bow and Horn bow are practical because they don't specialize in one particular thing. You could say that the Horn Bow specializes in speed, but I'd disagree at least in that you can go with the Tatar for +5 speed and only lose 2 damage, yet not many people really use the Tatar, why is that?
Explain to me, since this is the discussion section of the forums, why the Horn Bow is vastly more popular than the Tatar? If you choose the Horn Bow you gain 2 damage for 5 speed. Whereas, if you decide to go with a two slot bow, you could chose the Long Bow over the Rus, which gives you 3 damage for 8 speed. 1 damage per 2.5 speed compared to 1 damage per 2.667 speed. So the same ratio that makes people chose the Horn Bow over the Tatar is somehow not enough to make someone choose the Long Bow over the Rus. Gee... I guess the Long Bow is underpowered!
It's unused, not because it isn't balanced, but because the horn bow is the best 1s bow(Yumi is a HA bow, the missile speed makes it much less good for mid-long range shots) so the 1s bow guys use the horn bow, makes sense. As a 2s bow guy, if you chose the Long Bow, fast shooters like Horn Bow guys, are going to be impossible for you to fight against, unless you have cover. If you go with the Rus, fighting a Horn Bow user is a bit of a pain without cover, but it's still easily doable given they don't have too much more wpf than you.
So I'm not really seeing what the issue is, aside from that: You should be very careful when judging how good something is, by how often it is used.
Edit: Or maybe it's that this community is retarded and speed is so important that we should actually be seeing more Tatar Bows, because they're the truly OP bows?