Patolegend!
Fan of 1000 Arrow 'Slash
This is true, which is why it's so beautiful - there aren't really very many Ground resists in OU that want to stomach one of Slash's coverage moves (Knock Off/Aerial Ace). The main thing is it's gonna get some damage on something, and not hit air. I agree with other posters in that it would be a great Sand Spam team mate for Exca.Not that I'm shooting Sandslash down or anything (because it's a great submission and I love it) but people saying it could nab things like Talonflame, Zapdos, Thundurus on the switch are kind of forgetting the reality of that situation: it wouldn't happen. TA would completely replace EQ, so there's no benefit to switching them in. Obiously your opponent would expect a spammable move like TA, so they'd be switching in their Ground resists instead of immunities.
Now, this isn't a bad thing. Essentially what Thousand Arrows does is cut down the number of switch ins to a sweeper (which is cool because it's creatively done and really improves a shit mon). But let's not go around saying "Oh Slash can beat Zapdos now" because that won't be happening anyways.
By the way, those Hariyama calcs
The main issues would be relying on Rest Talk and the existence of Sableye, but it really could be tasty.