Earlier quoted context omitted.
Take the other job offer you said you have, give your notice, and if they give you an exit interview don't go into detail just tell them this didn't turn out to be what you were expecting and you got a different offer that is more in line with what you want.
> just tell them this didn't turn out to be what you were expecting I suppose my ego is getting in the way here; I really want to tell them how they have done goofed up but I also learned that such feedback is, 99% of the time, unwanted, so I believe your advice is better than what I originally thought I'll do. Thank you.
The problem is you giving honest and brutal feedback feels good in the moment but you never know when any connections you have will come in useful in the future, and if you will burn those connections with your feedback.
You don't stand to gain much by being honest on your way out, but there's a possibility of losing out if you are. So take the high road.