Max shutter speed on the 77d is 1/4000. The 80d is 1/8000 so that alone personally for me the 80d is my preference.
I just prefer faster max shutter so this is why I bought the 5dmk3 over the 6d. Also dual memory card slot. The 80 d also has a single slot so typically I do not use the 80d for hired events.
I really dig my 80d for functional versatility.
As mentioned before high MP full frame is not a minor difference in IQ. Sony and Nikon there is clearly a big difference in cleaner files in high iso low light shooting. If take my 5d4 filesany day over my 80d. However in good light the 80d is nice!!