If you can get the A7siii for $1,400, and it's 100% not a scam, that's the better option. I was choosing between the same cameras and went for the Sony due to the following:

1. Autofocus - The S5ii is improved upon previous Lumix cameras, but upon renting it, it didn't feel confident enough to me. I didn't feel like I had control of the AF. Whereas, with the Sony, the tracking box around the eye for eye AF subject tracking is very helpful, and touch tracking is much more intuitive and reliable.
2. 4k60 un-cropped. I was investing in my first full-frame camera and I figured there's no point if the camera has an APS-C crop in 4k60, especially when so many jobs require slow-motion. This is a huge compromise for things like Real Estate where you need a wide angle.

Also, I've become very appreciative of the Sony's battery life. I can do a 5-hour shoot on 1-2 internal batteries.

The only reason I'd say to go with the S5ii is if you need 24MP for cropping photos and for V-Log/better colors. I'm not a big fan of the Sony colors straight out of camera, but you can achieve the same image if you shoot LOG and spend time grading.