#1 - Why not build a rub bushing and place it 1/16" away from the outside of the wheel drum/cutter wheel. Put it at the point of maximum thrust. It will “push back” on the flexing cutter wheel and take up the overload. You could still overload the whole system - but we have to learn our limitations and respect them…
#2 - Here is what I was thinking about doing with my hay baler version:
Don’t let the cutter be on a cantilevered shaft. Build a heavy hub that slips over the output shaft and continue the shaft into a heavy pillow block so the axel shaft is supported on both ends.
The cutter wheel could be “traditional” like Mr. Waynes wheel drum design with the cutting edge on the side. Or, I think a stronger version might be: a cutter that is a heavy flat plate (supported by the heavy hub) of high carbon steel the cutting edge being cut out of the disk shape. This disc could be as heavy as you want. I’m thinking something like 3/4" plate. (The anvil is at 90 degrees from the “traditional” design.)
I think this would make an almost unstoppable chunker. It would last for a lifetime of DOW.