Eurostar has annoying pre-checkin times too though at least for London - they recommend over an hour.

I think that does make it faster to fly even with 2*airport to centre transit times - though extra time for checked bag in an airplane might just swing it back the other way.

If you could turn up for eurostar 5 minutes before, like a normal train it'd probably be better.

Also, a flight emits more emissions when ascending and descending than at cruising altitude, meaning that short-haul flights emit more per mile than longer ones. And a financial penalty on flying will act best as a deterrent where there are alternatives: one could conceivably replace a flight from Amsterdam to Berlin or Barcelona with a day-long and/or overnight train journey (especially if rail travel was cheaper), though there are few alternatives to flying to New York or Singapore other than not going. (If flights weren’t an option, a trans-Atlantic crossing would take most of a week and a sea journey to East Asia about a month. A train via the Trans-Siberian Railway, were it geopolitically viable, takes a week to go between Moscow and Vladivostok or Beijing.)