One photo in the report shows an obvious difference in roller face width between the FAG and SNR bearings. But the difference in face width alone may not be responsible for the different hertzian contact stress levels noted. The roller/race osculation ratios can also have a significant effect.
The M50 material used for aircraft bearing rollers/races typically allows a higher material reliability adjustment factor to be used in a conventional rolling element bearing fatigue life analysis than a race using carburized VIM-VAR 9310 gear steel would.