Sharpness of Canon 80d
If the stills look sharp and detailed, then the sensor and optics are not to blame. I would blame the encoder and whatever sacrifices Canon made for the video mode. The 80d has the same Digic 6 processor as the older and cheaper models like the T6i.

I have an older model T4i, and it is very low-res in 1080p mode, while in 720p mode it is chock full of aliasing, completely unusable. I presume Canon improved its cameras, yet Canon DSLRs are not known for being particularly detailed when used for video, you will be better off with a Sony or a Panasonic.