One thing's for sure, my Surefires work; even if covered in mud. And here's some proof about how well a Fenix light would work, after encountering some dirt....
https://www.candlepowerforums.com/threads/176954
Nonsense.
An isolated, selectively quoted product failure doesn't prove anything other than that a product isn't literally perfect. Applying this standard to Surefires would suggest that they are junk - look at all the posts about L1's that have have failed without being exposed to anything like this.
More, if one reads the thread:
I found out later the contact points were dirty and needed some wipe off my shirt. Got the lights back on but no more attention from my fellow cavers.
Hmmm. Cheap light, poorly maintained, fixed with a shirt-wipe vs expensive light, treated like gold, has to go back to factory. I know which I'd find more annoying - and likely to be fatal if pot holing, as that poster was.
In fact, do Surefire even quote a protection level against dirt and water ingress? Fenix do - and it's a very high one.