I always thought Freeman's hitting fundamentals were better than Heyward's, but that doesn't always translate into results. Freeman just has a much quieter approach and he opens up better and seems to meet the ball where it is pitched better than Heyward (even before Heyward was hurt).
The HBP really set Heyward back. Maddon usually sits him against LHP now. I haven't watched enough of Heyward to see what has happened versus RHP. My guess is he's still trying to pull outside pitches. Funny thing is his line-drive percentage hasn't changed at all. Along with the effects of the HBP, he's probably been solved to some extent through advanced scouting and analysis and he hasn't been able to make the necessary adjustments. Baseball is a very difficult game.