Quote Originally Posted by MammonAzrael View Post
  • A level 15 True Archer has a Base Attack bonus of +20/+15/+10/+5 (15 from levels, 5 from Eagle Eyes). We are currently at 4 attacks.
  • Haste adds an additional attack. (5 attacks)
  • Rapid Shooting doubles that. (10 attacks)
  • Multishot allows us 3 additional arrows per attack, for a total of 4 arrows with each attack, thanks to 20 BAB. (40 attacks)
  • And with just one more level we jump to 60 attacks in total!
  • At level 20 you're looking at 84 arrows!!! And you don't even need to use Rain of Arrows, that's optional.

Hitting your allies is next to a non-effect, as the area it covers is fairly small. CR appropriate enemies at this level will often be at least large sized (2x2 squares), often larger. And even with those that are not Large, nothing says they have to be at the center of the Rain of Arrows, meaning you can aim to have them on an edge, keeping your melee allies perfectly safe. Additionally, your allies (but not your enemies) will be aware of your preference to rain down arrows and should move accordingly.
You do know that the other attacks aside from the first and the one granted by haste are at -5, -10, and -15 to hit respectively, right?
And that adding three arrows gives another -8 on top of everything to all rolls to hit?
It's practically a given that a -10 or a -15 attack won't hit. A -8 on top of everything? You won't hit anything with AT LEAST 3/4 of all your attacks if you're fighting monsters on your challenge rating!
YES you fire a TON of arrows. But barely any of them will hit. And if you end up fighting a ton of weak enemies that you can easily hit because you're so many levels above them, well, that's EXACTLY what the volley archer is for!

Also, using one rain of arrows for one monster is a waste. Rain of arrows only does the same damage you do with one arrow. It's for tons of enemies, not only one enemy.