I just travelled from Scotland to Munich via London and Paris and had a wonderful experience. But that journey cannot be done in 1 day. I reckon the cost (travelling first class except on the Eurostar, when I went standard, and booked as all advance tickets) was about the same as a business class ticket on LH from Edinburgh would have been. No way it can be done for the price of an economy Ryanair flight but that isn't the point of taking the train at all.

I will definitely take the train for similar trips in the future.

[I used Rail Europe to book the travel from London and LNER to book the travel between Scotland and London]