It depends. I have only tried it once so far with an epic pro. And apparently, sometimes you'll get a point increase in one category while sometimes you'll get a point increase in two categories, etc. But I'll ask around and see how others have trained theirs.
For my epic pro, I first used a max pro rare to level it from level 0 to roughly 24-25 and afterwards I trained him using commons and uncommons 1-2 levels at a time up until level 30. I ended up with +1 in BC compared to what was on the spreadsheet.
I was going to experiment with this further after the rivals event with the legendary and other epic pro I recently drafted.