I think I saw it mentioned in another post that the missed tackles stats are artificially high, and that some that are counted as missed tackles should not be.
EX: Player A makes contact with the RB first, then player B comes in and finishes off the tackle. Player B is credited with a tackle and player A is credited with a missed tackle, instead of both getting credited with assisted tackles.
However, I do agree that break tackle and tackle ability ratings need to play a larger role than they seem to now.