I'm not a western rider. But horses are horses. Your analysis is right on the money and so is your distaste for gimmicks like tie downs, martingales, and yanking or sawing on the mouth.
Even with a bridle and bit, a rider with educated hands and seat (no matter the tack) can get a horse to relax, lower his head to its natural level, and engage the back up.
I'm sounding like a broker record but this video really has some good visuals of how and why low and long works to relax the animal, engage his back, and connect him back to front.