I'm going to read book next week before I can make opinion about the author.

I don't see anything wrong with weightlifting in fact it's a staple of my training, the problem with most fighters is how they approach lifting. One good book I found on the subject is "Expressing the Human Body" which is compiled from Bruce Lee's notes and diaries.

You approach exercise with specific goals, you factor in intensity (work-rate), the duration and the exercises. I don't see anything wrong with flys as long as your goal isn't to increase the poundage. Flys is particularly an isolation exercise for the chest which you should feel straight stretch in you chest when your arms are at the lower position.

Also don't underestimate stretching after your workout, it keeps your muscles supple, and as a cool down it helps you recover from a hard workout.