If you are already on the edge of the tread and need to lean further to do an avoidance/line change you crash. There is no reserve grip past the edge of the tire.
Not true. Anytime you are using all available tread on a public highway you are at 10/10ths regardless of speed. You can attempt to spin this anyway you want. You cannot compete with physics.
I'm thinking you must be new to riding, or have a lot to learn.
On the street I'm not hanging off dragging knees and elbows, with nothing left in reserve. I can be on the edge of the tire, at relatively low speed, and alter my body position on the bike, and speed up or slow down to alter my line.
So yes it IS true, I or anyone can be at the edge of the tread, at low speed, and have plenty in reserve to alter my line just by changing my body position on the bike, or braking or accelerating.
On my sportbikes, with their very grippy tires, you can be on the edge of the tread, and be nowhere near the available grip limit. Being at the limit of grip, means I'm racing on a track.
Seriously, get some instruction in advanced riding. The skills you learn may save your life. Chuckwalla Raceway has some advanced riding classes available.
I recall one gentleman who came out to a track riding class I was assisting in teaching. He said he felt he was wasting his time at the start of the class, and that he had 30 years of riding experience. At the end of the class he stated that what he had prior to the class was 1 year of experience, 30 times.