To be fair, sound has never been DTG's forté, it is already vastly improved in TSW compared to TS1. And with the TSW2020 update, it also seems to work as intended now. A lot better than before in any case.
Sounds like whoever made that video has synchronised a sound recording with a single stream video. Think about what's possible in TSW with variable angles, Doppler shift, long, short, variable etc horn use... It's not as simple as "get a recording and replay it" Not saying that TSW sound is good, that's one thing that really will improve with the editor!
Definately, and I think people also realise now how much effective sounds really build the immersion factor. Heres hoping
Immersion is one thing, another is realism. And last but not least, many locos/MUs/coaches are just a joy to listen too! Be it the screaming of a heavy US diesel, the singsong of a Taurus, or the gentle rumble of the DoSto coaches and the grinding moan when their brakes are applied. (The latter still doesn't convince me in TSW btw :p )
It seems to me that sounds have improved significantly since CSX:HH. Not just Peninsula Corridor (and ignoring the GP38-2 horn on that one), the M7 has really good sounds, and the British vintage diesels are all pretty nice, although admittedly I also don't really know what those sound like IRL. Not perfect, of course, but definitely better than TS.
A little off topic, but why does my GP38-2 horn keep breaking after I honk more than twice? Happens every time.
I think the GP38-2 isn't the only locomotive that has this issue, the german onesdo as well. I think its a feature, but I cannot say 100%