>>Overpowering a plane really isn't the issue. Over/under controlling the airplane is the issue.

I agree with that.

>>Weight and balance is really no big deal.

I think weight is big deal. All other things equal, light airplanes go faster than heavy airplanes. At level flight (1 G) the heavier airplane will have more drag. This will affect the speed.

When you turn, you may get up to 5, 10, 15 Gs or higher. Now, higher weight has a huge effect on the speed and handling.