Part of the advantage to a FF system is I would say is that you need to ETTR less for fast moving scenes with bright highlights since your noise threshold is lower.
It seems carved deep in many people's beliefs that FF has better IQ than any smaller sensor, no matter what technology is involved. Let's make things clear:
in the 6D you need to ETTR more to avoid shadows noise than in the E-M1. The D750 beats both the 6D and the E-M1 by a good amount (in the case of the E-M1 this was expected according to the difference in sensor size):

This means that if in your application ISOs over ISO800 are not involved, you don't need to ETTR more on the Olympus than on the Canon, despite the Canon sensor being 4 times larger.

It also means Canon sensors today have lost the dynamic range battle. Tomorrow, who knows?. A FF sensor is better than a smaller one only comparing equivalent technologies, but technologies vary from one brand to another and from one year to another.
My personal opinion is that with today's top sensor technologies, the only two strong reasons to prefer FF over smaller formats are the ability to achieve shallow DOF and the possibility to use legacy 35mm lenses in their native focal length. Image IQ is now secondary for most applications vs size, weight, price, lens availability, second hand market,...
Regards