c) the better quality photo made with the a7r which is not too bloody big or heavy to have it with you.
This thread is mainly about lenses, so let me note that if you only carry the A7R _body_, you won't take any photos at all --- so let's include some _lenses_ in the kit size comparisons.
When you want significant telephoto reach, some comparisons could be
- m4/3 with 40-150 vs A7R with ?
- m4/3 with 75-300 or 100-300 vs A7R with ?
- m4/3 body with mount adaptor plus 50-200/2.8-3.5 vs A7R with ?
Small kits based on small bodies with big sensors but reasonably small lenses mostly work well on outings when one or two wide-to-normal primes are enough.