Used to be, decades ago, just show up and go to the plane like it was a bus. Some dude would take your luggage and throw it into the cargo hold.
You'd be boarded and gone in 15.
When landed, they'd open then cargo hold and hand out luggage.
I had this experience in a transfer to a prop plane in Mexico. Fast, easy, quick.
What's most stupid about security for rail passengers is that the original fear from 9/11 doesn't even apply - you can't hijack a train and crash it into a skyscraper!
London had terrorist attacks from the IRA long before 9/11, including attacks on the transport network. There were 13 in 1991, of which 4 were on trains or at stations.
The new delays are for the passport checks. What used to be ~10 seconds for each EU citizen — is the passport/ID card valid and does the face match? — is now 60+ seconds for British people entering the EU, as the official must check they haven't stayed more than 90 days in the last 180 etc.
Hint when they ran a BART feeder to SFO the first thing the TSA did was start patrolling BART with drug dogs and arresting people for having pot.