And Eurostar is 1.) Far more pleasant than (in particular) budget European airlines and 2.) Not much longer downtown to downtown (and less for some routes like London to Brussels). Similarly in the US, I basically never fly from Boston to NYC or NYC to Washington.
I admittedly am not optimizing for price--intra-Europe flights can be pretty inexpensive--but I'd much rather take the train than fly even if it costs a bit more and takes a bit longer.
The main portion is 6h of train against 1h30 of flight. Door to door is a few more hours in both cases.
I understand the feeling. I hate flying too, in particular cheap European airlines. Gotta admit that there is an inflection point though, maybe around a thousand kilometers, where trains are struggling to keep up.
The main portion of flying isnt the 1h30 of the flight, it's the 2 hours getting to the shitty suburban airport then 1.5h going through security if it is busy, then 1.5h flying, then another hour getting from a shitty suburban airport to the destination city. Compare with just getting to Kings Cross and walking through passport control in ~20 mins, then disembarking in central Paris.
I commuted monday-friday from London to Paris for a couple months, and if I were to fly I don't think I could take it.
If you were flying daily then you'd have to be doing something terribly wrong to spend 1.5h getting through security - with airline status it should take minutes at worst, and even without status LCY has pretty minimal waiting times.
I agree south of France is probably borderline by train from London. Germany probably is as well. Likewise, I won't usually take the train from Boston to Washington DC. Just too long a trip under most circumstances even if the prices were comparable.
It depends on the speed of the service of course but, even with relatively high speed rail, a thousand kilometers is probably at the outside edge of where a train makes utilitarian sense.
European rail companies have claimed rail can be competitive for up to 4 hours, which matches my impressions of these journeys. London-Amsterdam and London-Frankfurt (which DB were talking about running at one stage before the problems with the new ICE models - don't know if that's still planned at some point or not) make sense, but that's about the limit tbh.
That feels about right and would seem to be consistent with both my own preferences and my observations on the Acela in the US Northeast Corridor. The two halves of the corridor (north and south from New York City) are heavily traveled by train and a lot of people prefer the ~3.5 hour trip to flying.
However, my impression is that relatively few take it all the way from Boston to Washington DC. It's still about the same 1 hour flight that the shorter legs would be by air but now it's basically a full day of train travel. I've done it when I've just been happy to work on the train but it doesn't really make a lot of sense most of the time.
Even with a train service like the Shinkansen, getting from Tokyo to, say, Hiroshima is over a 5 hour train ride for a distance of a bit under 1,000 km.
I like taking trains in Europe and Japan but there's an upper distance limit for when they make utilitarian sense. (For London to Brussels or Paris though, it's hard to imagine why I'd want to fly even if it were a little cheaper.)
Admittedly my experience has been "door to door" where door 1 is within half an hour's travel of Kings Cross, and door 2 is a hotel in downtown Paris / Brussels. So the differences between "downtown to downtown" and "door to door" times are minor.
Plane can do faster and cheaper door to door.