This is the exact reason i steered my business into bread and butter work 5yrs ago. installed an mot bay (best thing i ever did (other than getting garage assistant) i either farm out the large head jobs or just turn them away, i have a superb mobile autoelectrician with most dealer kits for in depth diagnostic work. So 90% of our work is now service,mot brakes and general repairs. If i can t do it and by some chance our sparky cant then we just send it to the agents.
You simply cant keep up with everything going on its not possible with every marque of vehicle or financially viable.
I think you either go down general servicing route and kill the headache jobs

specialise deeply in 1 or 2 manufacturers and invest in dealer tools

Become a diagnostics only garage doing few mechanical repairs

Or i think an untapped markey will be becoming a mobile diagnostic specialist just doing work for independent garages around a decent general area.
my autoelectrician charges me £60+vat for 1st vehicle and £50 thereafter on same day vehicles. he will probably get through 10/12 jobs a day from garages only.

sean