Dolphin created the 21Bis FM as best as possible based on charts and his own experiences. He combined the two resulting in mixed feelings from users.
The FM went through so many changes because (although a simulation), he wanted to keep a fun factor in it. The 21Bis is not an easy aircraft to fly at all, despite its simplicity in the cockpit. And he took that into consideration, so he adjusted the FM. Yet, user still complained, so he adjusted it more to user likings; and thus other users complained because it may not be to their liking. So he adjusts it again, and the same continues guys.
Then there are the users explaining their results based on manuals, hear-say, videos, etc. Or even their own experiences as maintenance crew. Although great research is being presented, it does not always beat a pilot's experiences. And that's what Novak wanted users to feel. How a pilot does. Not only is he a pilot, but he trained others, and I'm pretty sure he put the student through their paces.
Now...ED asked for flight Data. So he flew the real aircraft and recorded actual data (cross checked with DCS 21Bis), providing it to ED and proving that FM is at it's best. ED cares greatly about the FM of any aircraft in DCS. In the past 6 years, we haven't heard anything from ED regarding any FM errors.