Originally Posted by Fat DougJustDoug
To make an ability specifically targeted for one single move doesn't make sense. Competitively, it's viable. But, it's not like any other pokemon ability. Imagine an ability that didn't affect evasion in general, but specifically Double Team only. Who would make an ability like that? Someone who plays competitive battling Pokemon exclusively, that's who.
To target Stealth Rock as a specific move is just announcing that we really aren't making a general pokemon here. But instead, we are making a laser-precise tool to be used in the competitive Pokemon metagame. If we're going to do that, why are we bothering with pre-evos and dex entries? Let's just come up with some movesets and put it on Shoddy. We don't even need a sprite...
Except that Stealth Rock is a specific field effect, whereas evasion is a stat. I don't care if you increase +2 defense from Iron Defense or Acid Armor, it's the same net effect and the game doesn't care how you do it. Likewise, if there was some move not called Stealth Rock that had the side effect of causing the field effect Stealth Rock (for example, if Rock Smash had a 20% chance of laying rocks on the opponent's field or something), then this would still prevent against that, too. Field effects are different than specific moves, so your Double Team comparison doesn't make any sense.