The answer is simple: rent or borrow one and see how you like it! This is an area where no one but you is qualified to answer the question of whether the GH5s is the right camera for you.
Things to consider, in no particular order:
1.) you don’t HAVE to shoot in 4K if you don’t want to, even on a 4K-capable camera.
2.) the GH5s’ 10-bit 4:2:2 codec contains more color data than the C100 Mk II’s AVCHD 8-bit 4:2:0 codec.
3.) the GH5s will probably stomp the C100 Mk II in low-light. That could be really useful at a wedding.
4.) But you’ll have to sell all your lenses and get M43 lenses, or a Speedbooster for your Canon lenses, or a bit of both, to account for the M43 2X crop factor.
5.) And you’ll need to get Panasonic’s XLR adapter and a good mike, so factor that into your cost.
6.) but you’re not just using the on-board mike on the C100, right? If you are, shame on you, never use the on-camera mike–you should have a shotgun already that you just move over to your next camera. Whatever built-in mike the GH5s has, it will suck just as much as the C100’s built-in mike, so what’s the difference?
7.) if you want to fly a camera on a gimbal, the GH5s will probably be easier/cheaper, since its small size would allow for a smaller stabilizer.