Another alternative is using the QUERY function;
=ARRAYFORMULA(QUERY({A2:B, COUNTIF(A2:A,A2:A),COUNTIFS(B2:B,"Win",A2:A,A2:A)},"Select Col1, Sum(Col4)/Sum(Col3) Where Col1 Is Not Null Group By Col1 Label Sum(Col4)/Sum(Col3) '' FORMAT Sum(Col4)/Sum(Col3) '0.00%'"))
.