Is an avg. ~25 mpg a problem?

2016 M6 Touring @ 107,000 miles.

I’ve been in a long time battle trying to my to get my mpg higher, doing essentially almost everything except taking it to a full fledged shop, and I just cannot seem to get my MPG higher than an average of 25, even if it hovers ~28 for a few days. I do ~75% city (maybe more) with ~25% highway, and the 25mpg is just driving me crazy.

Things I’ve tried:
- Changing air filters
- religious 5k oil changes
- the lightest feather foot ever
- italian tuneup (for 20 seconds) once every oil change
- Correct tire air pressure
- Checked for no visual mechanical issues
- Had my oil change mechanic check the MAF sensor
- Lighter weight in the cabin
- Learned good use of manumatic mode

Is avg. ~25 MPG for 75% city driving normal? Should I relax?