Pretty much exactly like your reasons for leaving. I was a mythic raider as well.
Mythic guilds having a hard time filling the roster, it’s main appeal is catering to casuals who log on 3-4 hours a week so it’s pretty dead, friends lists are empty for the devoted players, Devs talking about removing neck level requirement on Azerite gear cuz the system is so flawed and stupid, balance is at an all time low, combat is super simple and clunky - feelsreallybad… So many issues that shoulda been worked out in beta.
I’m not going back either, it’s not worth it trust me. It’s a mess.