What is it you dislike about the G80? It's what I'm currently using and have been considering an 'upgrade' - which would be more of a side-grade if I'm honest. My reasons are simply to try something else, always wanted to try some Canon lenses they have great options for the budget shooter. I wouldn't personally go back to Nikon, had 4 of their cameras and a tonne of their lenses through the years, I got really bored of the overall experience shooting with them. But, I did enjoy using them at one point. They might work better for you, we're all different and have our own personal taste.
I was looking at the 80D, I thought it might be much better at higher ISO [though I rarely go above 1600 with any camera] but it's not, they're very samey up to 3200 if you compare them. You wouldn't want to use either above 3200. The G80 is very comparable to APSC in general, don't let the hype about bigger sensors get to you. M43 files are often sharper, remember too the G80 has no AA filter on the sensor which helps with that. If you are going back to dslr you might want to go for one without that filter too, or you may well find your images a tad softer.
Fuji are great, I shot Fuji APSC for a couple of years and they are very good - better than most APSC offerings, at higher ISO BUT ... when there is noise it can be horrible, sometimes weird patterns and harder to clean up in post. I would wait on solid reviews on the XT3 before jumping at it. You could get a D7500 and a nice lens for the money.
Again, point out what you dislike about the G80 and maybe you'll get better suggestions. The camera is only the controls, good glass and your own artistry are far more important, though it is best if you're using gear that you can be comfortable with. You will be giving up IBIS, that brilliant touch screen and unless you go with Fuji's smaller bodies or Sony A6***, size and weight too. And with those options you're giving up comfortable grip.
I think dslr has plenty of life left in it, there's pros out there using 10 year old dslr who don't give a fudge about flappy screens , 4K or evf and they get the job done.