On the specific question-- Harvey is a much better player than Franco. Franco is a very marginal UT, Harvey will be a very decent starting 3B by the end of this season.
On the general question-- the aggregate splits are more important than contact, but they're TWO ratings, and control is ONE. If you level that playing field:
20/75/75/75/75 is a league-average hitter, but can't start at a corner; if he's got 50/50/50/50 defensive ratings he's just a sub.
75/75/75/20/75 is a very good lefty-masher, if he's got 50/50/50/50 defensive ratings he gets 200-250 very solid PA in an OF corner.
75/75/20/75/75 is a starting player at any position, gets 400-450 PA, just needs a platoon partner of the sort that can be found cheaply in FA. if he's got 50/50/50/50 defensive ratings he helps you win a championship.
The bottom player is MUCH better than the top 2, and I think the second player is slightly more likely to help you win a championship than the first.