This is from my (original series) IL2 experience and what I was able to see/hear from the YT videos:
There is no denying that both the original and latest IL2 sounds aren't accurate. They don't sound like the Merlin or Daimler Benz engines we are used to hearing from YT videos and flight shows.
However... when put in the game context - to follow engine physics, damage, fly-byes etc, they do the job far better than any other moded sounds I've ever heard. In other words, they serve their purpose and get the job done. Moded sounds are great, and have come a long way. But still not up to the level they should be IMO.
Now, mind you I am sort of an audiophile (audiophile wannabe would probably suite me better
), so having these stock sounds is in no way satisfactory from my point of view. But, with what they had - not having big enough budget to fly their sound engineer to UK and record them, they did a darn good job. At least the in cockpit sound (engine) is very much believable.