You will have access to C and B airports by calling the ATC facility and requesting a deviation from ADSB requirements.
You MIGHT be able to do this once or twice, but from what I've read, it you use it to get out of ADS-B you'll get a paddling. It's supposed to be to get to a shop that can install the units. So far I have not heard of anyone getting a nastygram.
I know you can zig zag all over and miss airspace
You might want to look at a map. LOTS of non-ADS-B area out there. I can fly PA->FL and maybe add 50-100 miles to get around a Mode-C veil and some Class C's. Thing is, transit through a Bravo is never a given, even with VFR corridors. And for me, the major PITA is the DC area with its own special rules to transit.
The 10k altitude restriction seems arbitrary, why 10K? Why not up to Class 'A'? Mode C worked fine for decades. IIRC Centers do have *some* ADS-B integration, but that high up Radar LOS should be pretty good.