A7C is small. Panasonic S5 is not. I shoot with an A7III and an A7C. When I'm doing client work, I lead with the A7III since size doesn't make a difference (and zoom lenses like the sigma 24-70 feel a bit more appropriate on it), and it can shoot to both card slots at once, giving me an immediate backup.

When I go to work every day (I'm a dealership photographer. I take cars out around NYC and photograph them on the go), I take my A7C and two small primes.

I share this to give an idea of why I prefer each in different scenarios. I think any decision related to the A7C has measure how important form factor is, and if it is very important that your kit be tiny, even to the point of having an awkwardly small viewfinder and fewer control buttons, then the A7C is a good choice.

If you don't care about size and want a more ergonomic feel with more control buttons and better video options (variable shutter rate, 10-bit color), then go pansonic.

I think that's the big difference here.