I think physics should play into this more than the rating. The tackle rating should just be how good you can make a tackle like open field tackles and so on.
Me personally believe it should be up to the physics to determain the type of hit the devfensive player can dish out.
If anything the Hit power rating should play a factor, but most of it needs to be physics, becasue without that you have people laying each other out constantly and big hits aren't that common thats why i'm not surprised when it happens beacause it happens so often.
There needs to be more wrap up tackles instead of knock you out like its the last day of school hits. The Big Hit a type of player can dish out should be all about speed, momentum, weight and hieght, angle, Hit power, etc.