What if Slaking gets very good moves and doesn't get nerfed

True

What if he is nerfed or super slow and turns out just as useless as any normal type? When he is released either you find him or not and either he will be strong or Salamance or metagross or someone else will be stronger. In that case get that one

There are many ways that they could nerf Slaking, and they definitely will do something. If they wouldn't leave Mewtwo and Ho-Oh, then they are not going to leave something that will be much easier to aquire, much higher CP, and placable in gyms.

Nerf or they should include abilites somehow. However I don't see his high CP being that much of an issue other than he will probably be in every gym.

Experienced trainer will still manage to beat him.

If they nerfed Mewtwo, they will nerf Slaking somehow. If it's not in the stats, then to be truer to the game, they could give him a very slow fast move and introduce an extremely slow charge move.

Slaking also gets scratch, zen headbutt, and body slam, so it could be even powerful than your conservative prediction. Scratch/hyperbeam or body slam would be ultra-broken.