Sorry TotalBeginner but I think you're actually underestimating the professionalism of some of the people that work as PSAs handling no-frills airlines, and no doubt you will but a stress on the word some. I make it clear as part of all of my announcements when boarding flights, which I believe is necessary to please have your photo open to the photo id page it doesn't take long to look at the photo, the passenger, then rip the card, it's acheivable with 25-minute turnarounds (I've never witnessed 20-minute turns), although I will admit that I usually feel like a sitdown, and a little sweaty after I've done one. Even with the relative discomfort, my main concern is not safety, it's that I've been barking orders at pax, and some passengers who may have been rightfully deserving of a priority boarding placement were not given one, as I was rushed.
We're quite fortunate at my base where we have three gates where passengers have got to go down just three steps before going into a holding pen, standing at the top of the stairs rather than at the podium is usually the best way to ensure that you can check everyone's passport & boarding card. We have another two where the gap is so small to enter the gate area that people come in single file, again a benefit to us. However, whilst these physical restraints benefit us, it can be done from others. It's all down to the training & commitment of staff, and no I'm not a manager or supervisor!