“he switched to new bridgestones and it was sliding all over”
Did he switch to Bridgestone YLC’s?
If you are going to compare different tire manufacturers, you have to make sure they are similar compounds. The MG yellows would be comparable to bridgestone YLB’s. Last time I ran a set of YLC’s( prob 4 years ago), I was sliding all over the place, not even close to the mg yellow.
If you have a soft compound front tire and med compound rears, your going to have a bad over steer.
And to answer your question, absolutely theirs such a thing as to much grip, especially in the low hp classes.