Actually, this subject and the reasons, 'Why' haven't really been covered. Firearm safety rules are never genuinely useful as long as they remain nothing more than mental safety rules. In order for any firearm safety rule to work it has to become an everyday personal habit - One that is instinctively NEVER violated.
If someone who's disassembling a Glock hasn't first racked the slide, at least, thrice and then locked it open for both visual AND tactile inspection, well ...... he's made a serious firearm handling mistake - One that clearly violates the user instructions in Glock's Owner's Manual.
If someone who's working on a Glock, or any other pistol, covers his own hand with the muzzle then he needs to start learning basic firearm safety all over again. Obviously, he missed one of the really important points about firearm safety the first time around. (Cooper's Second Safety Rule: 'Never allow the muzzle to, so much as cross, anything you are unwilling to see destroyed.
Anytime someone discharges a sidearm in a toilet, the mistake belongs entirely unto that person and his misplaced trigger finger. The only exception is, maybe, when a pistol is being reholstered and the edge of the trigger catches the side of the holster; but, this is an extraordinary circumstance. It's far more likely that the user's lazy or forgetful trigger finger is the real problem.
You don't need to go to a, 'low ready' position in order to prepare to reholster a Glock. You should IMMEDIATELY remove your finger from inside the triggerguard and place it along the side of the frame the moment you stop firing and begin to look over the top of the slide. (If you've been trained to hook the distal joint and place the tip of your trigger finger on the edge of the triggerguard in the same way that Ayoob and I do - Fine! Just remember to be consistent.)
If you wait until moving to, 'low ready' before removing your trigger finger from inside the guard, then, your pistol shooting reflexes have not been properly conditioned. (I watched a shooter do this just the other day. That delay, no matter how brief, can be lethal!)
The OP is correct: Glock pistols are NOT as safe as they could be. I could write a post several pages long on, 'Why Not'. (But, I won't!)
In fact I live with a Glock pistol, just about, 24 hours a day. Neither do I fault any of my Israeli acquaintances who have been trained and are required to carry all of their personal sidearms in C-3. Inside a civilian residential environment, C-3 is often (But, not always) the safest method of regular carry.