As someone who has recently had two very bad shop mechanic experiences, I can certainly sympathize. But I've had very good ones too, so I wouldn't cast aspersions on the entire bike shop mechanic industry. Sure, they all need to pay the bills, but some still very much take pride (and are good at) what they do. Unfortunately it's a learning experience...which can be unpleasant as my last two were...to learn good from bad.
But like gurk007 I'm also accumulating shop tools at home and watching tons of both Park Tool videos, as well as other resources. I have successfully changed rotors, cassettes, bled hydraulic brakes, changed handlebar and stem, pedals, bar tape, seat posts, brake pads, saddles and chains. I have aligned pads/rotors, and done full adjustments (H/L limit screws, B screws, physical alignment) of both front and rear derailleurs--mechanical and Di2/eTap. I can do basic maintenance like clean the drivetrain (both quick-clean and deep-clean). I have installed and seated tubeless tires. I wanted to be able to do all of this because 1) I want to know how what I ride for over 10 hours a week works, 2) I'd like to extend the life of my bike and associated parts by taking care of it.
The last things I haven't tackled, but will do once I am able to buy the tools, is install a bottom bracket and crankset. I also haven't serviced hubs and bearings, although I have upgraded the ratchet in my DT Swiss 240 hub from 18 to 54 tooth--that's the closest I've come to hub work.
That said, I trust the good mechanics I've run into (and will avoid the bad ones now that I know who they are) so if for whatever reason I can't do the job at home, I have a short list of people I won't be afraid to take my bikes to.