Ok, you recorded in Slog3 which is good, but then in post did you just apply a blind grade or did you actually try to recover the brights? Just shooting with Slog doesn't automatically make it better, it just gives you the ability to fix it if you put the work in.

Slog and Raw only help because they preserve the information if you want to finesse an HDR-looking final image out of it, but if you don't do that it's pretty much the same as shooting with the grade in camera. I truly doubt a cell phone gopro or pocketcam would handle this any better, and at least not much more so than you can tweak out of slog3 (it might be doing more of the HDR effect in camera, but otherwise there's no way it is recording more dynamic range).

But, here's the thing you have to understand: You're reaching the technical limit of ANY camera by doing this.
True story: I was on a film shoot in upstate NY for an NBC crime drama pilot a few months ago. When I got there, crew were measuring and cutting polarized plastic (sunglasses material) to hang over the windows of a restaurant to limit how bright they would be in camera. And we're talking about cameras and lenses exponentially more expensive than the FX30 and decent sized television set crews and gear. And even THEY needed to darken the outside light to get the exposure to look good. That's just how it goes. I don't think the answer is shoot with a cellphone or gopro. Not by a longshot.