I work in a software development company for almost two years now, and I'm planning on quitting soon. The reason is that I cannot stand my supervisor (let's call him John).
TL,DR: Should I tell my boss (who was the one who recruited me) the reason I quit is my supervisor John's behavior and how inefficient he is, or just tell them that my career goals changed? The other reason is not a lie, I want to go to university full time and it is impossible for me to keep working for my current company, even part time (my financial situation can handle it, I made a lot of savings).
John was the scrum master of our team when I first got here and we had the same boss. Since it had not been long they started working with scrum methodology (and I had quite a bit of experience due to past jobs), I tried sharing all the information I had to improve the management methods. We were losing way too much time on meetings for useless reasons (for example, we had 30+ min stand up meetings for a 5-6 dev team, which is simply too much, specially when we are doing simple tasks). We even had a meeting with the main scrum master from the company and he agreed with my suggestions to avoid losing time. However, John decided not to implement any of the suggestion, since he doesn't "want to change the way things are done now" (even though it's still new...).
I told myself that if the company wants to lose time, fine, at least I tried. So I continued putting the same efforts (even though I was new in the team, I was already considered one of the top devs of the team, due to my high delivery of user stories) and my boss was very pleased. As time went by, I realized that our scrum master was very narcissistic; he always keeps talking about himself and all the tasks he is working, even though he doesn't even complete any US (in 4 sprints, he has completed maybe 1/4 of the US he committed, while the rest of team completes about 4/5 of the US they commit). And that pissed me off, because he just wastes everyone's time. We even had multiple arguments about this; I tried answering questions he asks during meetings to speed up, but he told me in private that he wants other to answer even though he knows I know the answer, because he wants them to participate.
Recently, he even got a promotion and is now the boss of our team (while still keeping scrum master role). I would've love getting that job (who wouldn't?), but I think that other team members deserved it more than him. And that promotion was the cherry on the cake for me; he now has even more reasons to talk about himself and all his meeting and how important they are, and thus, we lose even more time in meetings.
A couple months have now passed and I gave a lot of thoughts about it and decided to go to university to get better job opportunities and so, I decided to quit. While that reason alone should suffice my boss, I really want to tell her that the supervisor she selected is not a good fit for the company and it's damaging productivity. I know one or two members that deserve that promotion more than John. However, I feel like stabbing someone in the back, something that I do not do. Don't get me wrong, John is a good person, he is kind and caring, he just is not fit to be a good supervisor. Should I tell her that reason when giving my notice or not?
Edit: This question is different from this one, because I will not be telling my supervisor my those concerns but to the HR person. That way, they can decide what actions they'll take, if they do.