As the others said, Masters classes seem to be for those who have the main part of the technique down and just need minor improvements. (heck I blew up my shoulder trying to keep up with the big boys)

All four strokes (well count out fly for me) help you improve the feel for the water, break things up a bit and for backstroke, indeed gives you some power. Flip turns are a nice to have. But playing wall tag with swimmers way beyond your level is frustrating and will get you nowhere.

You have to have pretty good technique to swim any amount of yards breathing 5x. The coach may have been impolite but honest in his assessment
Consequence: speak to him: either he's willing to observe you do tech drills in another lane, according to your own plan, and help you improve your technique and endurance, or you need another teacher. An intermediate-advanced freestyle class would be good, does not have to be TI, but some of their drills are very useful (some I hate dearly).