No, if a Deepwood Sniper isn't dominating, he just isn't really trying that hard, nor being played very smartly. A well-built DS, played smartly, kicks all kinds of arse outdoors where opponents suffer from cover and such that the DS gets to mostly ignore, thanks to feats and special abilities. Only time the one I saw was really in trouble was when fighting the dragon a second type, after it very narrowly fled for its life the first time with single-digit HPs remaining by the time it finally got out of that SOB's absurd bow range. The DS could only miss on an extremely low attack roll, until the dragon was one or two thousand feet away, then he finally had to roll mildly well to hit, until it finally left his maximum range.
I was the DM at the time (temporarily, as the regular DM was busy). The party had just about finished fighting some of the dragon's minions, who had tried their damnedest to stop the archer (including summoning flying critters right next to him) and still they got trounced, when the dragon dropped below the forest canopy and attacked. It blasted, clawed, and snapped at the monk and rogue, rendering one unconscious and the other nearly so, and then the Deepwood Sniper began hammering it with several arrows per round; at that rate of fire, he got a critical hit in at least once every few rounds, as I well recall (I know he scored close to half a dozen critical hits before the dragon finally escaped).
The archer was already mildly or moderately wounded by the time the dragon attacked, but managed to stay out of the dragon's reach until, as it nearly got within biting range (still couldn't use its breath weapon again just yet), it realized that all the arrows he was hammering it with had already gotten it nearly half-dead at least, and it still had several other nearby adventurers resuming their attacks against it. One of whom had already summoned some hippogriffs to chase and attack the dragon, and then proceeded to Call Lightning against it. Of course, the party's druid had only just begun to attack it when the dragon had gotten close to the archer; before that point everyone besides the archer was still busy finishing off the last few dangerous minions, or was preoccupied with trying to guzzle down enough healing potions to save themselves after the dragon's breath and savage melee assaults.
Finally the dragon fled when it realized that, although it may manage to kill the archer first, it too would perish if it stuck around much longer. The archer could ignore cover pretty much, thanks to his feats and whatnot, while the dragon could not, and the dragon had seen clearly enough that its minions were defeated and unable to support it against the other adventurers. With the druid finally able to turn his attention against the dragon without being grappled and mauled by the summoned critters of the kobold spellcaster (whom he had finally managed to slay), the dragon was in trouble, seeing as how the Deepwood Sniper had already planted a dozen or so arrows into its face and back, rendering it half-dead. The dragon fled, going above the trees and then below and back again and again as the archer just moved a bit higher or lower in his tree each time, plinking three or four arrows into the dragon every round, dishing out ~10 damage per alchemist's arrow (often more, after enhancements and strength were factored in).
The regular DM had allowed him to gradually acquire one or two quivers full of alchemist's arrows, crafted by the party's transmuter wizard who had good Craft (Alchemy) skill (these arrows are in Sword & Fist, and I think they were reprinted in A&EG or something...). I couldn't just overrule something the regular DM had allowed, and arbitrarily take away the alchemist's arrows already accumulated; I was only taking over temporarily while the regular DM was busy. Even without the alchemist's arrows (which ran out within 2 or 3 rounds of the dragon's escape attempt), the archer only would have dealt about 2 damage less per arrow; the dragon still would have only narrowly escaped (just with around 25 HP instead of around 5).
When the party went after the dragon the next day or so, after expending some charges from wands and such to heal, the dragon charged the Deepwood Sniper and tried to maul him, but the party's casters were already prepared to defend him. The dragon couldn't get a hold of him, and the archer always carried spares since he was used to his bowstring snapping at the very least. He had a large supply of essentially freely-enhanced arrows (he could Magic Weapon them, and the party's wizard GMW'd them anyway beforehand IIRC). The wizard lost his familiar, polymorphed into a hydra, and a few other party members were savaged, but it did delay the dragon from finishing off the archer, long enough for him to receive healing and begin his arrow barrage.
The dragon's kobold minions (including a wizard and a cleric both of mid-level) harried the party and made things difficult, but PCs had quickly intercepted the casters, so neither could really reach their dragon ally to heal him or anything. Though the archer was badly mauled in the first round, the party got him mostly-recovered very quickly and kept helping him escape the dragon's melee reach so he could fire more and more arrows. Mid-level parties are hard to beat when they're playing smart. With Freedom of Movement and other enhancements from the casters, the Deepwood Sniper was able to keep escaping and firing more arrows. The dragon's allied casters were already intercepted in the first round and unable to do anything about the archer. Nothing the dragon and his allied casters could do wasn't beyond the PC casters' ability to dispel or otherwise counter, or the Deepwood Sniper's ability to just ignore thanks to feats and abilities, like Improved Precise Shot and True Strike and Greater Magic Weapon.
In this second fight, the dragon was unable to escape or triumph, since the PC wizard just kept hurling Baleful Polymorphs, Phantasmal Killers, and suchlike at the dragon after his familiar was slain, and the PC druid kept hurling fire and lightning spells at him along with 1-2 of his best Summon Nature's Ally spells. The rest of the party (monk and rogue) kept the kobold casters busy and slowly managed to kill them. The dragon barely made his saves against most of the wizard's spells (the fact that both BP and PK allow two saves was the dragon's salvation; the one time he failed a save against BP, his kobold casters managed to undo the polymorph, since the dragon made his Will save to retain his mind and abilities, though turned into an iguana for 1 round). The dragon got in 1 or 2 breath attacks during the second fight, catching the Deepwood Sniper and I think 1 other PC (the druid IIRC), but both made their saves for half damage and survived, with the druid healing them for a few rounds after each.
Though the Deepwood Sniper only contributed about two-thirds or three-fifths of the damage to the dragon in the second fight, it was still enough to kill the dragon after the rest of the party's attacks, and the fact remains that in the first fight, the DS reduced the dragon to single-digit HPs pretty much all by himself (the druid got in, IIRC, one low-rolling zap of Call Lightning damage, and his summoned hippogriff or two got in only a single weak attack past the dragon's AC and DR). The second fight was in the dragon's cave, and that's the only reason the Deepwood Sniper was in trouble for most of the fight, but with the party's casters helping out, he was able to stay out of melee reach most of the time and fire 3-4 arrows per round for about 9 damage each on average (plus, of course, the few really nasty critical hits).
I used good strategy and tactics for the most part in both battles, though I won't bother recounting every little detail here (only problem in the first was that I had the dragon drop down and maul the monk and rogue, standing almost right next to each other, first, rather than the archer; and that's only because I wanted to give the party half a chance of victory rather than a certain TPK; the PC wizard was Silenced during that battle by a kobold caster, and thus couldn't help the archer escape grapples or whatnot; in the second battle, I just didn't have the dragon maul the wizard and druid first, as they would have died in 1 or 2 rounds for certain, and I'm no RBDM so I didn't want to kill 2/5ths of the party, and the most tactically important 2/5ths, right away; the archer would not have repeatedly escaped melee if not for those 2 PC casters). Any RBDM could easily slaughter a party with a smartly-run dragon if he felt like it, of course; but then, if the PCs aren't being given even just a small chance of victory, it's not really a game, just an egomaniacal power-trip by the DM, being a total @$$.