Well, I would not begin to make the foolish claim that one is the better character than the other, not without much more extensive reading and actual use in play at least.
1)Range wise, yes, of course it's unlikely that you would be fighting at a range that allows you to bring the full power of archery to bear. However, being a stealth oriented character, it results in uncertainty as to where the attack came from, giving you more rounds to snipe from cover to cover, or even using allies as cover. The melee rogue on the other hand, would be that much more obvious a target, and of course, would not be participating at the same kind of fight that a warlock(who is purely ranged, abeit shorter). Again, the stealth issue here is paramount
2) The main point of using a crossbow would be to avoid ever being within 'challenge' distance of opponents, where the best solution for an artful dodger rogue at that point would be to brave the AoOs and get behind a defender, or to use a disabling attack at melee range(with a missile weapon if necessary) and proceed to leave the immediate vicinity. Well played, the target would be beset by ranged attacks coming from an indeterminate square, even within a closed scenario, and with the damage difference between warlock and rogue, he should be bloodied or even dead at lower levels, though at higher levels, the padded sumo effect kicks in and you might want to have someone like a wizard or a warlock to disable the target while you blow away chunks of hp.
With the stealth, note that the numbers I mentioned are at the beginning of a rogue's career, and he'd obtain double digit stealth modifiers about the same time the first of the monsters begin to. It's not an invulnerable cloaking device, it's a tool to buy a few rounds of risk free damage to get the edge. Notably, the levels you start getting monsters that can see through a stealth check reliably is also the level you get powers that lets you remain concealed without one. They can and will retaliate of course, but thats a couple of rounds of easy damage. Effort spent locating your rogue is effort not spent hurting the rest of the party, and mayhem will ensue.
In the end, my personal preference as to the more effective character does lie with the warlock, except his character role is ill defined, rather than a pure striker, the warlock serves best as a controller with striker attributes. Your own anecdotes with the warlock say as much, you're mowing down minions and using your Armor to inflict unavoidable damage over time while the use of the warlord's abilities is an admirable use of team strategy, using the Armor on it's own against non minions lasts briefly due to the temp hps(and you) being smashed in close combat.
I'm defending the rogue purely in the role of a striker, not in terms of overall power. You want lotsa point damage? Look no further. But if you want to do more than that, the warlock, the wizard, have more offensive options than just inflicting lots of pain.