Maybe yours is just "Super Stock".
For a "seasoned mechanic" I'd have thought you absorbed the limitations built into a stock R3. They don't spin the tire and they don't slip around corners under acceleration. They built 'em that way on purpose.
There are a few little things that need to be done before the greasy Metz shows it's weaknesses. After the "little mods" you won't be drag racing Harley's, HOT ROD or not ... you wouldn't bother.

Whats a tweeked Hog put out anyway? ... 125hp and 90 ft lbs? That's probably about what a stock R3 puts on the ground in 1st-3rd gears, maybe a little more.
We are talking about using the bigger contact patch on a car tire needing to stick upwards of 150hp and 158 ft lbs to the ground in FIRST GEAR! But thats after the 1st gear power reduction has been eliminated and the bikes overall power has been restored to it's full potential.
And I don't check the "bikers handbook" each time I use the brakes either, I grab what I need, when I need it, from wherever I feel it should come from. 90/10-70/30-50/50 never crosses my mind ... but when the 240 rear Metz can't handle any serious brake application without locking up and sliding at higher speed, then it's worthless to me as a brake. Many times I've used the same amount of force I applied earlier at slower speeds where it worked fine, only to have it start sliding for no reason. I don't like that feeling. It feels .... unreliable.