Ignore the "two" cameras. This lens is softer than all the other lenses ive had, or have, on my 60D. If i didnt have the 5DMKIII (the reason i got the lens) the Tamron would have gone back within about half hour. If i can use a Canon 17-55 f/2.8 IS, a Tamron 17-50 f/2.8 wide open on it i would expect to be able to get the same results from the 24-70 f/2.8. Even a second hand 18-55IS ive just brought is sharper wide open.
Im not comparing the lenses as such, just expecting then all to be usable wide open.
Try doing the focus test through live view as I detailed. That will eliminate the possibility of the issue being one of focus calibration.