Most trains I've commuted on (in the Netherlands and Germany this is) weren't like that 9 out of 10 days. How well you can work differs per line, year, time of day, and type of train, but overall I'd agree more with GP than with your experience. Both exist, of course
Sure. That's a very biased way of looking at things. RBs/REs, and even S-/U-Bahn are likely to have ample seating even during "rush hours" in most of Germany. But it sounds like you've never seen cities like London during rush hour? Tubes are tightly packed with people. Even if you get a seat, it's unlikely you'll feel comfortable bringing out your laptop. I've got a friend who does indeed commute ~50min to Cambridge by train and gets some work done. But that's rather the exception for a city like London. Many people will have similarly long commutes just being stuck inside the tube with little space to maneuver.
I'm sure you can find more big-name examples like London but that some of the biggest cities out there are packed neither invalidates everyone else's experience nor should be a major surprise methinks. Probably more biased than looking at how the remaining 95% of the system runs? Of course, either extreme is biased
And anyway, saying you can be productive in a 30 minute train ride comes from the same mentality that says you can knock out some work "between meetings" when your calendar is a swiss cheese of meetings.
It's not nothing, I guess, but it's sure not any kind of productive focus time, even in the best of scenarios.
