Well in Master's swimming most coaches are just there to give you a workout. They are not there to coach on you on how to swim. They are also use to generally working with people who were competitive swimmers in HS/College and who understand all the pool lingo and are use to working out in the pool. Ya know?
It sounds like you need to get a private swim coach to perfect your stroke. Anyone who wants to swim as an adult, and swim laps... needs to do this I think.
As for what you are doing helping you with open water swimming... as long as you get some practice in open water... pool workouts translate to open water fine. You can read my 3 mile open water swim RR... and I'll tell you that to prep for that I did 2 workouts a week in the pool (the bulk of my distance) and 1 in open water (only :45 minutes). It translated just fine for me.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"