Why would you travel with a flat battery if you know you'll need your phone upon arrival? Almost all planes are equipped with charging sockets these days.
when we sat in the blue chairs, some nice staff came and helped us to prepare all 4 documents in our hand (including the phone with QR on screen), so no need to go through anything at the counter. Just go, show and pass.
scanning the QR code on paper or on phone take the same amount of time: a fraction of second. How do you know they were slower when everyone was at a different booth? Are you Hawkeye 😂
As I told you, Thailand pass on phone was that the majority of passengers had when I arrived last Monday, it was fine. That's the aim of a QR code by the way.
At Bangkok airport you need 4 documents to be ready: