What if I told you that only having one or two boarding groups is probably the fastest way to board a plane, but because "full service" airlines need to provide benefits for elites and partner elites, and be able to sell early boarding as a revenue stream that they have all these boarding groups that slow things down?
Back in June and July, I was in Australia, and flew with UA partner Virgin Australia. They call boarding 30 minutes before scheduled departure, and have three boarding groups - Preboarding for those with disabilities and those who need extra time, business class (including elites seated in economy), and then everyone else. 15 minutes is about all it takes to board a 176 seat 737-800. No row numbers, no separate main cabin boarding groups. Just everyone goes. The overhead bins filled up just as they do in the US, and the plane sits for a bit with the door open until it's departure time (sometimes they leave early!).