68 is probably a little low, but it is hard to argue. Tannehill will probably have decent speed, and such but not on the level of others like Cam, or RGIII.
But you are definitely overrating a lot of our players..
Wake, Long - yes
Starks, Carpenter and Fields are maybe deserving of 90s or high 80's.
Why would Daniel Thomas be 80+? Gates 70+? He caught like 2 passes? I doubt Jimmy Wilson gets that much of a buff either. Rookies often don't get rated very high for mid round picks either so above 70 would be great if they really were.
Looking at last years ratings, Gates was a 69, I'd say he has improved atleast 1 point. Jimmy Wilson was also a 68. D. Thomas was a 80 for sometime before he got injured.