The ID expiry check is done at check in and not whilst boarding.
With rgds to 130+ pax in 20 mins, if you can do the job quickly then it can be done. I was 10 mins late to a gate once, boarded the flight and still closed it early.
I was the only person in our team to not use the tannoy as I found that with so many announcements being made, nobody listened to them. Instead I stood half way down the line of pax and said what I had to say at the top of my voice. They all shut up, stood and listened and the boarding procedure was nice and easy.
You need to be fast to do a decent job.
At check in, if you insist on charging excess baggage at every given oppurtunity then you won't close a flt on time, simple as.
At the gates, if you insist on scanning everyones ID with pinpoint precision then you won't close a flt on time.
You also need to be ahead of yourself with rgds to missing pax. As soon as you know who's missing, get the bag numbers and get the ramp guys looking for the bags. If they are still missing when you are ready to close the gate then it turns into a race between the pax arriving and finding the bags. Basically don't leave it until the end, get it done whilst you can.