This is photography and consumerism at its worst. They are so busy checking the latest lens tests, they don't have time to learn how to use the lenses they already have. You can spot them because they are excited about the new lenses or camera they just bought, instead of the wonderful picture they just made. Two notable factors seldom discussed are flare variations and lens performance at different distances. Superb performance at infinity can easily change to so-so close up performance, and vice versa.
Bad focus equals lower resolution Vibration, shutter or mirror vibration means lower resolution.
Yes, your lens testing results can vary camera to camera because different cameras have different vibration levels. This means if you have five different bodies of the same mount, the results from the same lens may vary due to body vibration. Flare within the film chamber lowers resolution. Contrary to popular belief, cameras can vary considerably with this little discussed variable. In the mid 70's Fujica marketed a line of 35 SLRs with the mirror box flocked in black matte material.