I have both the a1 and the a7s3 (three of them) for almost 3 years now. I use all of them (a1 and a7S3) at the same time at the same event (track and field or cross country high school races) but for different requirements.
For the a7S3, the 10bit 422 60fps 4K cannot be beaten by the a1 at the same setting. Overheating in a7S3 occurs only if in direct sunlight at 90 deg. F. Fix for this is a little shade.
For the a1, I need the 8K30fps at 10bit 422 for two reasons why: (1) the 8K allows me to shoot at 1/1250 sec so I can extract 12MP photos for hurdles (see here: https://youtu.be/iYqCFQoRqRY?t=291) and sprints; (2) With 8K30fps, I can crop in 200% without dropping below 4K output. This allows me to record while riding an e-bike using a 50mm lens that in post looks like I have a 50-200 zoom. see here: https://youtu.be/eg332N-sYwg?t=55
A1 does over heat even at 70 deg. F. The fix to A1 overheating to allow for 6-8 hours extended recording is here: https://www.youtube.com/watch?v=IFqYIwcExS4