Looking for suggestions and personal experiences, my 3.5 yr old son is developing a quite severe stutter, it has me feeling defeated

Looking for suggestions and personal experiences, my 3.5 yr old son is developing a quite severe stutter, it has me feeling defeated Venting wall of text incoming, sorry. I have a pair of 3.5 yr old twins, boy and girl. They were both delayed in their speech (fairly common in twins), and we started basic speech therapy when they were around 2. While my daughter is still delayed, she is progressing and I'm in no way concerned about her future development. Around 9-12 months ago, shortly before finishing the 6 session therapy course, my son started developing a stutter. It started with just the "I" when he started sentences eg. "Iiiiii-i want cheerios." But the speech therapist said it's common and not necessarily a true stutter and more like his mouth trying to catch up to his thoughts. So we continued the basic speech therapy where we focused on proper pronunciation of sounds like S, H, and F. The problem persisted, worsened, and started happening with many many sounds, not just the I's at the start of sentences, but multiple words/sounds throughout his sentences. Now our newer speech therapist thinks he developed his stutter specifically because of the previous speech therapy we had him in. Constantly hounding him about the S, H, and F sounds, like we were told to do, somehow fucked his development up and created these mental blocks he now struggles with. So now we have completely pulled back on his pronunciation and just encourage him to speak freely. We've been told to always let him finish through his stutter, and then repeat what he said to us. My wife does 10 minute alone time with him every day where she rates his stutters and then he does 10 minutes alone time with me (but I'm not as involved with the actual therapy, it's just fun time we spend together where he doesn't have to compete with his sister). And we've started praising the (few) times where he has smooth speech. The stutter just seems to not be getting any better, and almost seems to be getting worse. It's at its worst when he is agitated or hyper, and when he is competing for attention with his sister (something I personally think contributed to the problem to begin with). We now make sure to tell our daughter to let him finish before she takes her turn speaking. My wife is an early childhood educator. She was the one that insisted on us starting speech therapy so soon. I always maintained that I thought it was unnecessary, and that they would overcome their delay with time. I never considered it would cause more harm. But I wasn't going to stop them from going though, my wife is slightly more educated in this type of stuff, and I wasn't going to forbid her from doing what she thought was right for our kids. But now I have relatively serious resentment towards my wife for pushing so hard for this when it seems like if she just listened to me, instead of flippantly dismissing my opinion since I didn't have any formal education in the matter, we wouldn't be in this situation. As much as I know I should, I haven't brought up this resentment directly with her, as the whole thing is still fairly fresh, and it's just going to dissolve into fighting and crying. I figure she has already pieced most this together and feels bad enough. So far, all I've said is that I feel defeated and like a failure as a father, and that I would have so much rather he had been a little delayed than having such a severe stutter. So she can probably read between the lines. I'm extremely concerned about his future in terms of bullying, his ability to make friends, girlfriends, etc etc. He has friends now, but they are so young and not at an age where something like this affects their relationships. I've only met one grown person in my life with a proper stutter, he and I were both young adults. He was a supervisor at the movie theater where I worked my first job. And while he was relatively well liked by the workers, there was definitely unkind remarks made behind his back and a general attempt at avoiding conversation with him as it was a little tiring trying to converse with him. An extremely similar feeling to how I feel when my son's stutter is at it's worst. Again, the best word I can use to describe how I feel is defeated. Sorry for rambling on. I've just been needing to get this off my chest for a few months. I guess I'm just looking for suggestions, anecdotes, personal experiences/stories, do's and don'ts, what I can expect as he grows older and enters proper school, whatever support you may have.