Sorry! It's another "What camera?"question.

[noone]

2 hours ago, hmcindie said:

A7s has horrible lighting artifacts with led lights. You can see them here too in the left corner. It kinda is a bummer for otherwise a great lowlight cam (as a lot of low-light venues tend to use those led lights that clip horribly on the a7s)

Actually, I think that left corner is down to the smoke coming there (I used to like smoke but have come to hate it lately      The light was changing rapidly (and varying in intenstity greatly too) and at other times was very different in colour.

I have looked at this shot on four different computers and the red colour varies on all of them (very red on the one i am using now, less so on the one i posted it with).      If the A7s has a problem with any lighting I think it is more blue it has an issue with but even that is only some situations.

[deezid]

Go with the GH5 and keep the lens (or better invest into Sigma 18-35/50-100 lenses and an EF-Speedbooster for cleaner/sharper images and more range).

The GH5 is easily usable up to ISO3200 (or 4000) unless underexposed in both Video and Photo if sharpening and NR are turned down to -5.

I agree with @JordanWright about the 3 stops less lowlight capability. But a clean and usable F1.2 aperture easiliy compensates for that.
ISO3200 (4000) Limit on the GH5 vs. ISO25600 on the A7s2
F1.2 vs. F4.0 basically. Not too bad. Try to focus using anything faster than F2.8 on a Fullformat camera... lol

And the GH5 will show more fine grain with lots of fine detail (10 Bit codec) while the A7s2 will look washed out at high Isos with bubbling appearing starting from ISO12800 when underexposed and ISO25600 when properly exposed.

Forget about using Canon cameras if you concerned about low light or even Video AND low light.
ISO800 is the max for an APS-C style Canon and 1600 for the 5D MKIV and 3200 for the 5D MKIII using Magic Lantern. The GH5 will still show way more detail at ISO3200.