I don't think it's meant to let you replace all car trips you could possibly make with a single 50 euro payment per month.

Nobody in their right mind would, yeah. So they just have to pay for the train if they don't want to buy and maintain and fuel a car for such journeys. Myself, I'd never consider going by car between such well-connected cities, I'd have to drive (can't read a book for those 5 hours) and deal with parking and either rent or borrow a car (or buy, I suppose).