70s definitely makes it into the OF if it is "squared up". So much is depended upon size of field, competition, level of school, etc.
If you hit 75 off the tee as a sophomore, you will probably get cut in large class California, and be all-state at a small school in Delaware.
What exit velo in the 70s does is prevent extra base hits, and give little margin for error at times. However, it will still get you in the lineup at some places, using a variety of factors. But I highly doubt there are guys that hit it 75 that are going D-1.