“Because I got one of the Rockstar keys and it won’t work with the Steam overlay no matter what. Downloading a Steam copy now…The game was advertised as a Steam key and I got a Rockstar key, I was unhappy with the fact that I didn’t get the Steam key I had purchased but I would have been fine with it if I could have at least used Steam features by launching in Steam. I can’t do that. The company does not want to refund me, so I’ve started a dispute. There is nothing shady about what I am doing, I gave them and the situation the benefit of the doubt and tried to get it going. I’ve already purchased the other key and I expect that PayPal will resolve this in my favor.”
You shouldn’t have uninstalled like that. If you’re getting a Steam Copy you should have Brought on Steam, then copied your Game folder across and then installed on Steam. Steam would have recognised existing files that match (which would be most) and then you’d have less downloading.
Simplified Slightly: You’d need to figure out if Steam has any change in the folder format (wouldn’t be major) than the RockStar installer. If you’ve not got fibre, markets are saying it’s worth investing the 5 minutes.