I gotta jump in on the side of the cleric archer here. My first 3E character ever was a paladin turned cleric archer. I ain't sayin' that +20 to damage ain't great, but ya gotta suck 20 points offa yer bab ta do it. Sure yer primary attack is gunna do just fine, as is the second one ya get with rapid shot, but by the 4th and 5th attacks, yer gunna be in real danger of missing. The cleric has +6 from divine favor, +5 from his magic arrows (GMW), and an addtional +5 from his bow (GMW again) so right there he has got +13 ta hit AND damage (assumin' the Peerless twirp has his +3 arrow ability workin') that the PA can't access.
Now it is safe to assume that by 20th level everybody will have a +5 mighty bow, and we can assume everyone has a great dex and an 18 strength, so lets break it down a bit.
20, 15, 10, 5 for the bab. -2 for the rapid shot leaves you at
18, 18, 13, 8, 3. This will be where they both begin. Assumin equal dex, both having weapon focus, equal bows, so we weon't even bring those numbers into the equation.
Takin' his power attack with the bow, PA looks like this:
-2, -2, -7, -12, -17 but we can safely assume he is doin' 8 points more per hit (as the other factors equal out, (specialization can be had if the cleric takes the aforementioned level of templar))
If we give both example characters a 28 dex via whatever method ya want, weapon focus, a +5 bow, bracers of archery, and point blank shot, (ain't handin' either character magic arrows cuz face it, how many people can afford to pay 50000 gp for every ten rounds of combat for +5 arrows) so we can add 18 to each bab.
PA gets up to +3 arrows right? So we will give him that. So we will add +18 to his scores.
19, 19, 14, 9, 4. If yer shootin' at a 30 ac (not a really difficult ac for a CR 20 encounter) you can really only count on 2-3 hits and that may be pushing it. So if we calculate +4 str, +3 arrow, +5 bow, +1 point blank, +2 spec, +1 bracers, +20 from power attack,
we land on +36. We'll give a high average of 5 damage per arrow for 41 points per successful hit. Averaging it out based on bab we come up with (for simplcity we skip crits):
20.5, 20.5, 10.25, 2.05, 2.05 for an average damage of 55.35.
Cleric comes up with all the same damge bonuses the PA has minus the power attack. To this he adds Divine Favor and +5 arrows stead of +3.
44, 44, 39, 34, 29. So only missing on a 1. Cleric's average damage comes out to 29 per successful hit.
27.55, 27.55, 27.55, 27.55, 27.55 for and average damage of 137.75.
Add to this the fact that the cleric can heal himself several times per day, dispel magic, and do all sorts of other little goodies like flame striking and blade barrier, and fire storm. Plus all the other spells.
As fer cover, I'm thinkin' yer gunna run from cover when ya git hit by a blade barrier. Yer in a jungle getting pelted? Firestorm 'em all and let god sort 'em out. Yer in anti-magic? Course that is gonna suck, but the truth is it tends to limit all the players that way. Yer left with yer base bab, yer feats and yer base stats. Arcane archer gets nuked, PA is lookin' abit better than the cleric but only in bab and only if he aint power attackin'. Damage is going to stay balanced cuz he can't power attack without all those other bonuses to hit. (not that he can all that well with them)
Long and the short of it is yer peerless archer is cryin to his mommy cuz he can't hang with the big dog.
-Immort