The only speech therapist I've had focused on a lot of strategies for releasing tension in your mouth and vocal folds, which included some of the things you mentioned, like diaphragmatic breathing. We did a lot of stuff with vowel prolongation which was really helpful for me. My therapist also wanted to do a psychological approach by practicing self-disclosure and learning to live with a stutter. So I guess I went through a combination of what you did. This was really helpful for me, but I really had to keep up with practicing the strategies otherwise my fluency would fade.