It depend on your morphology I guess: for me below 15km rides, I can wear jeans and it’s fine, but above that it starts to be painful. When I’m touring I really enjoy having my cycling pant, even a cheap one does the job perfectly for me. But again, I have a quite large distance between my ischium bones, so the same may not apply to everyone.
As a French living in Germany, I often take the train to visit some friends/family. I would say it’s working well from Frankfurt to Lyon or Frankfurt to Paris and not too expensive if you have a Bahncard and you can plan your trip in advance. But IMO, it the least we should expect from 2 neighboring countries.
I’m very excited to see the resurgence of night trains though, I love this mean of transport in particular!