I think if modern multi grades increase life or reduce failure will vary from case to case, depending on usage. It obviously has advantages where temperature fluctuations are considerable, but may have disadvantages when the aircraft is used infrequently.
Mono's are heavier at lower temperatures & when the aircraft sits unused will tend to remain coating the internals for longer than a multi grade. Multi's as they remain thinner will more readily drain & leave internals unprotected from corrosion. I imagine that start up wear may be a concern with dry internals (is there any sort of oil priming on an aero engine?).