Sony EDU: Sony Alpha 7C Mirrorless Digital Camera (Body Only, Black or Silver)

A7c has much better AF and a fully articulating LCD. They share the same sensor, so IQ is the same. The a7iii has better ergonomics, dual memory slots and a better EVF. I picked the A7c.

As someone who switched from Canon to Sony by getting the A7iii and then later picked up the A7Riii, I have to say, for all the mud slinging going on here regarding the UI and from the Canon forums before I made the switch, it's really a non issue. You literally need 20-30 minutes to set up and customize "My Menu" and the Fn select buttons and custom buttons for your flow, and you never need to touch it again. It becomes second nature.

12MP is not a bug, it's a feature.

The camera is primarily designed for video, even though it has the full suite of Sony's still photography features.

Video has a far higher data processing requirements than stills. The higher the resolution, the more data that needs to be processed. The higher the data processing requirements, the more heat is created and the greater battery requirements.

The A7S III is a native 4K camera. For most video imagery, the camera is 4K in and 4K out. Most full frame cameras with more than 10 or 12MP resolution have to greatly degrade the image quality in order to record 4K video. They either crop in using only the center portion of the sensor, or throw away light that hits the sensor with pixel or line binning.

The A7S III uses the full readout of the sensor, and as native 4K, has low image processing overhead, creating low amounts of heat, resulting in long battery life, while not needing an internal fan. It has fast imaging pipeline, so provides low rolling shutter. And with it's comparatively massive sensels / photosites (image sensor pixels), provides exception low light capability. None of that would be possible in a similarly sized camera with a higher resolution sensor.

Pro stills photographers have compared the stills photos from the A7S III to Sony's higher resolution cameras. It's generally impossible to tell the difference unless pixel peeping or looking at poster sized enlargements. A number of photographers who largely deliver Facebook, Twitter, and other digital deliverables use the camera for both video and stills.

TLDR - 12MP is perfect for 4K video, making for higher quality video imagery in a small lightweight package. And if the photos are used for digital delivery, provides outstanding stills quality as well.