Contrary to popular belief, tornado shot is viable on league start.

I will level as rain of arrow until uber lab but you can pick up tornado shot as soon as you get 3rd lab on deadeye, hell you could even pick it up as soon as you get GMP support.

I use pierce and detached mirage archers as opposed to chain on a lower budget, this gives a very good damage uptime vs bosses. Many uniques were introduced or buffed in 3.19 that makes the leveling and early mapping much smoother.

I also supplement the single target with storm rain ballista although I found today that PoB was miscalculating the dmg on storm rain, which makes artillery ballista a strong alternative, with only 10% lower dps but no attached clunkiness to the skill.

Pob: https://pastebin.com/r5bUsvw2