Some lenses won't cover an entire full frame sensor. But a "4k" lens is a gimmick and a misleading phrase.
This is the kind of comparison video I don't like. If you aren't going to shoot charts and control the light, then everyone comes away from this video with their own special sauce opinion in their head. No insight on long end behavior or potholing. A waste of a day in my opinion.
That said, I'm not seeing a difference worth paying $5g over $350. Canon up to their ole sales BS again.