Well, EXCLUDING glitches. Warp is a debuff (Actually more than 25%), that also primes, which for Warp Ammo IV is +100% damage. +100% is better than +50% (AR is only +70% if you ignore the GOOD evolutions, giving up usefullness and variety for a small damage boost is stupid). But sure, you go ahead and have your squishy, underperforming character. That's the whole point of the game being easy, no? Can use whatever silly setup you like, have fun, and still "win".
Actually, warp debuff is 15%.
Warp ammo IV, when primed, is 120%, but only against armor or health. Health is a pretty small part of the overall damage you'll deal, and if you're up against armor chances are you're better off using AP for the multiple hits, as well as the damage bonus against armor, even though it's smaller. Not to mention the incredible bonus that shooting through walls is. Furthermore, and most importantly, warp is a debuff that hits only a single target every 4-5 secs, and is a projectile, meaning that it'll likely be dodged if used against humanoid targets (the most important ones). AR is up against anything you're shooting about 80% of the time. It's a completely different thing, and it's much more useful as a weapon enhancer.
Saying that the 20% boost to damage bonus evo on AR is stupid is... Well, ignorant and self-righteous, pretty simply. It's not stupid, at all. Given that in this game, with the right positioning you can take pretty much 0 damage, one could argue that the DR evolution is stupid, if anything. But I won't, cause I realize that both have different reasons behind them and will appeal to different players. Having been here a long while, I can tell you that the more experienced a player becomes, the more he starts to worry about his damage output rarher than his survivability, usually. Which ends up with taking evos such as the 20% damage boost over the DR. Quite simply cause his survivability is already granted by his skills and experience. I'm pretty sure you'll change your mind too, eventually

But even if you don't, there are very few builds and evolutions in this game which I'd call stupid, and neither of those two evos fall among them.