This was always the upsetting thing about Eurostar/Eurotunnel between UK and France. In my naive teens I dreamt of how wonderful it would be if we joined Shengen and could literally just hop on the train to Paris. But sadly we went the other way and completely left - and now it’s as bad or worse than any airport.
While the Eurostar pre-boarding times are not great, they are much better that an airport.
I usually arrive 40 minutes before the train starts moving, including large luggage (30 minutes before is the limit at which the ticket gates close).
There is no waiting for you luggage on arrival because you always have it in your hand.
This is also possible because the distance between check-in gates and the train is only around 50 meters in all 3 stops (London, Brussels, Paris). On those 50 meters you have the luggage scanners, passport control, and the waiting hall.
Compare that to kilometers of walking at Heathrow Airport.
