With Gore and Richardson, so far Richardson has 38 carries and Gore 33, so the carries are pretty close. However, I do agree that later in the season, which will be end of fantasy season start of fantasy playoffs, Richardson will probably be more valuable since he'll still be getting a lot of carries while Gore is splitting with Hunter and Jacobs and Gore will be resting more. So I actually agree with you that Richardson is probably a little more valuable.
Gates has been injured a lot the last 2 seasons and is already injured again, but is expected back this week. Vjack is gone, but Floyd and Meachem are there and getting a lot of targets. Gronk should get more targets, especially in the red zone, with Hernandez out for awhile, but should also get more attention from defenses with 1 less weapon out there. I think Gronk will be better and has a significant less chance of getting injured.
Overall, I think this trade is pretty even. Idk about you, but with such a big trade like this, I'd want it to favor me a little more if I'm gonna trade half my starters