Problem with Fenix 5 GPS accuracy

That isn't the problem, as has been discussed time and time again on these forums by people who have actually looked at watch teardowns and know something about RF engineering.
The bezel is part of the antenna system. The issues (and I'm not saying they don't exist) appear to be that it isn't the optimal length for the GPS frequency (the circumference should match the wavelength, and it doesn't), and that generally people run with the watch pointing to the side, so the most sensitive directionality of the bezel is not pointing at the sky.

Its a shame that (for whatever reasons) Garmin have made some design compromises that impact the accuracy of the GPS. Having said that the accuracy is still "good enough" for most recreational purposes that the watch was designed for. If I was buying new and had to choose between a 935 and a Fenix 5+ then I would take the 935 like a shot - mainly for battery life but also for slimmer form factor, lighter weight and better GPS accuracy. I could go back to using my 610 which with only GPS and no Glonass or Galileo manages a more accurate GPS track in most cases. If I did go back to the 610 however I'd have to forgo many of the other metrics that I've got used to plus I'd have to get back into the habit of waiting for the 610 to show me GPS accuracy of around 15ft or less before starting my activity.

Yes, I rather agree. My own decision would still be the F5, I think; at the time in the UK the 935 was the same price if you could find one in the first place, and my use cases make the unpainted metal bezel a good choice (I'd banged mine very hard off a rock in Norway within a week of buying it, scratching the screen protector but doing no other visible damage). The 610 track was lovely, but that was a square patch antenna in the thick section of the wristband, with better sky view than any current watches provide. Some aspects of the 5+ series are tempting (mapped elevations for one), but I am moving to races with cut off times of 12 hours and beyond over the next couple of years and don't want to take the battery life cut.
FWIW, personally, own use case, YMMV and clearly for many people does, I run with my wrist tilted in a bit to help the sky view, use a Stryd footpod for winding runs under tree cover which do short distance using GNSS alone, and find that the F5 degrades a bit faster in difficult circumstances than previous watches but is generally acceptable in terms of overall distance and lap times. Galileo+GPS is in the UK better for me than GPS alone, except for occasional bad moments (this would be seconds per 150 miles of running) where it scoots way off track.

@macbadger - Interesting - I hadn't realised that the 610 antenna was in the wristband. I generally find that my tracks even under trees are good enough with the 5+ - am yet to see what the OW Swimming is like though as the water's still too cold for me. I'm going to try GPS and Glonass for running when I have spent a week or so on GPS only to see if that makes a difference - I did find Glonass gave me a slightly better track on the 935.