Longbow isn't the best choice for dragonhunter in any gamemode with any build, it's a pity because the skills are interesting but lack any synergy with the rest of the kit.
Autoattack is fine. Good damage, cast time feels right, decent effect.
True shot is iffy, it's got a big punch on a low CD but it's pretty unreliable. Since you're rooted in place you can be easily blinded, blocked, obstructed, los'd, reflected etc.
-Increase the CD to 6s for all gamemodes and decrease the cast time to 1/2s.
Deflecting shot should be changed, as it stands its very clunky and requires heavy light to be traited to be really useful.
-Increase CD to 15s, make knockback baseline, increase radius to 180, decrease range to 900. Now you have a defensive skill on LB, something badly needed on a slow, long range weapon attached to a very slow class.
Symbol of energy should be changed significantly. Any build that relies on symbols, one of guardian's main profession mechanics, can't use this effectively. Even with the increased projectile speed it's very hard to land this skill on anything further than 600 range from you, good luck landing it on another player at all. Even when you do, the payoff is very low and doesn't feel worth the effort. The long burn stack is unappealing as is the vigor on a symbol that you probably won't be standing in.
-Increase CD to 20s, each tick of the symbol applies burning for 3s, remove the vigor, remove the projectile effect so it acts like symbol of swiftness. Maybe your character fires an arrow straight up that strikes the targeted location with holy energy? The projectile effect on this makes it awful in every game mode, that's the important thing to address.
Hunter's Ward is an okay skill. It really only needs sped up a little since right now you can just walk out of it.
-Reduce cast time to 2s, reduce cooldown to 40s. Easy changes.
Heavy light would need reworked as well with the change to Deflecting shot. The stability on knockback isn't really needed on dragonhunter. What is needed is a LB specific trait that has synergy with the kit.
-Heavy light reduces longbow cooldowns by 20%. Gain 120 precision, and an additional 120 precision with a longbow equipped. This would bring LB cooldowns from 6/15/20/40 to 4.8/12/16/32 when traited and grant 5.7% or 11.4% crit chance.
I think these changes would breathe life into the longbow weapon and playstyle while maintaining its identity and improving quality of life. None of these changes would increase power creep significantly, they would just make the weapon actually usable.