Yes, I've done a few tests with HLG. -- for some reason, if I bring the footage into a regular (non HDR) timeline in FCPX, the colors are all wrong and there's no easy way to normalize them
Have you tried HLG? Can't remember where I read it but someone was actually advising to bump up the in-camera saturation and take saturation off in post if needed.
Yes, I've done a few tests with HLG. With underwater shots, for some reason, if I bring the footage into a regular (not wide color gamut) timeline in FCPX, the colors are all quite a bit off and there's no easy way to normalize them. So I prefer using VLOG over HLG for that reason -- at least with vlog there's an easy official LUT to covert it to REC709 that will get you in the ballpark for color correction. But as I mentioned, 99% of the time I think you're just fine shooting in standard without any sort of log profile at all.
Regarding saturation, theoretically I think you'd indeed be better off removing saturation in post rather than adding it in terms of preserving as much color shade separation as possible. But the best option IMO on cameras that don't record in raw is to get the saturation in camera as close to the final output you want so you don't have to do any tweaking in post. That's why I prefer the standard color profile over CineD or Vivid/Landscape. CineD I find desaturates the footage in a way that looks unnatural for underwater shots and it's hard to get them to look good by just adding saturation in post. Conversely, Vivid/Landscape are a bit too saturated. If you reduce the saturation in post, you get a result that looks ok, but not any better than the standard picture profile IMO.