I compare the Sony a6000 and Sony a9 using the Sony 70-200 F4 and Sony 70-200 F2.8 G Master in both photo and video. Links to products below:
The Sony a6000 is a great aps-c camera that many have, but what happens when you compare it to a full-frame Sony monster, the Sony a9. Even more crazy is if you pair the Sony a9 with the Sony 70-200 F2.8gm and pair the Sony a6000 with the Sony 70-200 F4. I found from my experience comparing the two cameras and lens combination that Sony a6000 photos were very sharp with the F4 lens and the Sony a9 with the F2.8 lens was also very good and sharp.