As a revenge killer, your main goal is to be able to outspeed and kill a pokemon, given a free switch in. Weavile doesn't need to be able to OHKO pokemon to act as a revenge killer, and also doesn't need to have bulk. All you need is to be able to kill common sweepers
quickly, so that they don't sweep your entire team. Ghost and dark are both phenomenal offensive types, so they're useful in killing popular offensive pokemon, like Choice Band Dragonite, Garchomp, Zygarde, Gengar, Alakazam, Salamence, Aegislash, etc. It doesn't need brute force to be effective, it just
needs speed. I won't argue with you that its power can be underwhelming, but that alone doesn't mean it isn't good.
Lastly, its coverage doesn't suck. Low Kick is a very helpful move with great coverage. It's most often used on heavy targets, like Ttar and Heatran, so basically you have a Close Combat as coverage that doesn't cause defense drops. It's worthless on light pokemon, but how many light Rock, Steel, Dark, or Ice pokemon are in OU?
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TRC., and other proponent's of solely the All Out Attacker set: I moved the SD set to other options, as it generally is way too frail to use it, and slashed Ice Shard with Pursuit on the CB set. What do people generally think? Should a CB set just go to OO as well?