And that's the point. When shooting from a 'typical' standing retention position, the gun is on the side of the body and will be canted slightly using the thumb as an offset to allow the slide to cycle. In an ECQ scenario there's really no telling what position you could have to fire from. For example, it's possible to have to bring the gun out across the body and fire such as in a car-jacking situation or in particular, grappling entanglements.

Here's an example of a pretty standard standing retention firing position...starting at 1:30


From a student who took a ported Glock to a Shivworks(Southnarc/Craig Douglas) ECQC course...

"Run my GLOCK19C during livefire and having some issues with the muzzle blast during several positions. I have to switched it to a regular Glock19 after my nose and mouth was bleeding."

Source- AAR: Shivworks ECQC Sacramento 10/5-7/12

ECQ scenarios and having to fire from a compressed or retention position while entangled or otherwise engaged with an assailant are very common occurrences during civilian defense occurrences. Anyone is free to disagree and dispute that as fact, but the stats demonstrate otherwise as does practical experience and common sense.

With that being said, is the possibilty of vented gas from a ported handgun causing affecting vision by making contact with the eyes, the primary concern in an actual defense scenario? - Absolutely not...and I never said it was, but it is nonetheless enough of a tangible potential problem that it should still be a consideration(albeit somewhat of a relatively minor one compared to other factors)and is easily remedied by simply selecting a non-ported model as pretty much every single personal defense instructor recommends.