I haven't driven the X3M and M340i back to back, but as a very new owner of an M340i (2021 MY -- I know some 2020s had issues), I can address your list of things you don't like about the X3M from the standpoint of the 2021 M340i:
- No android auto (2021 M340i has it)
- No remote start (2021 M340i has it available)
- Rough ride. Really unpleasant on bad roads. (Since the M340i uses the M Sport suspension, and not the M3 suspension, it is relatively compliant and comfortable in comfort mode.)
- It's a dog from a launch unless you use launch control. Really laggy (M340i is not laggy at all, but there is a little gap at initial throttle tip in.)
- Randomly changes radio station on me (Haven't had this problem -- sounds like a defect.)
- Handling is weird. Too twitchy (Nothing weird about the M340i -- handles somewhat similarly to the e90 and very responsive, but steering is numb.)
- Fuel tank is too small for a car that gets 16mpg. Like 225 mile range. (M340i gets sufficiently good mileage, so no problem here.)
- Apple carplay works 50% of the time (This was a big problem with some of the 2020 MY 3 series, but it seems to have been fixed after a 7/2020 update to iDrive 7. Mine has never failed in any way.)