When I use Finn's Editor, I do notice that almost everyone has power as their run style. I am speaking of Franchise mode, 4 years in. In my previous Franchise which I ended due to long sim times, I also noticed the same thing with Finn's Editor. It's as if the game resets the run style of the player.
When I am in the off-season, I edit the rookies through the Edit Rookies feature. The game generator normally generates CB's, FS, SS players as finesse. RB's are normally a mix, WR's are mostly finesse with balanced and power runners showing up now and then. DT are mostly balanced, DE's are rarely ever unbalanced, as are ILB's, OLB's, Offensive Linemen, TE's and the Kickers. For me, the game generator does a decent job with the run styles in the off-season.
However I use Finn's Editor during the season and couldn't help but notice that nearly my entire team were power runners.