I can understand Midas frustration. As a player I have for a very long time been annoyed at the current performance system in the game. While I am not so much bothered about the actual difference of a specific aircraft type, I was very much annoyed that all AS aircraft can fly much further than their real counterparts. AS currently does not take into account reserve fuel, headwinds, slightly longer actual flight paths (compared to the great circle) due to take-off/landing, holding patterns, etc. The range/performance obviously also doesn’t degrade over the age of the aircraft, which can influence the actual range quite a bit.
On the other hand I am very much with the team (as I have previously worked on that as well). When a new aircraft is entering service, it is (or at least was at my time) often difficult to find reliable data (i.e. ARJ21). Or in case of the Embraer E2, I was never able to find the manuals at all. So when players are screaming for a new type to be introduced to the game, not finding reasonable data (Boeing just wouldn’t release MAX data in their manuals), and trying to fit the aircraft somehow into the game to make it reasonable, it is like an impossible task. Then there are a bunch of (older) aircraft that have wrong values. If you try to fit in relatively a new aircraft type, you sometimes have to skew actual values to make it fit. The alternative would be to adjust the values of older aircraft (for which data might not be available anymore), which then affects enormous fleets in-game that suddenly have different performance and wrecks havoc with existing flight plans.
So, is the C919 in AS not 100% correct to the second comma? Most likely, yes. Can you make it exactly match the (latest) performance data published? Definitely not. Unless you can bring comparable and real data for ALL other aircraft in the game too (good luck with that). Even the data published by Boeing and Airbus is not comparable 1 to 1, and good luck finding data about all the other smaller and more exotic aircraft out there.