The problem in MSB is not the sound recording, it is the way the sounds are mixed and equalized being a big problem.
I believe this is just a ‘copy and paste’ description which is listed on every TSW Steam DLC. It’s a bit misleading however it’s always good to watch livestreams and read reviews before purchasing anything.
The problem with MSB and the rest of the Preserved Collection is that something in the port over from TSW2020 borked the sound mix.
True, even the dostos have some horrendous sound in TSW2, i mean you can hear the noise made by them from the loco cab with windows closed. The sound coming from the passenger coaches for German trains sounds like freight cars and drowns any little sound that comes from the locomotive itself. In TSW2020 the sound was much better although it did have some occasional looping problem.
Just because sounds (notice it doesn't specify all sounds, just generic plural) were recorded from the real thing does not necessarily mean they will be accurately implemented or sound good in-game. It's just typical marketing; it is not a lie but it is not the full truth either. Cheers