does a frac rig benefit
because the mainsail supresses the jib's tip vortex,

no.

or does the jib
vortex hurt the drive of the mainsail?

yes.


Yes, the benefit is from the greater adjustability of the frac. rig.

lots of advantages to a frac rig, but suppression of the tip vortex of the jib
is not one of them.