I guess the frustration of some users is about the gap between expectations and reality.
The product was announced to contain loads of features. Little details were published before release so expectations with regards to the quality of these features ran wild.
In addition, this very complex piece of software was expected to run flawlessly on release, which it did not.
Now customers are expecting the developer to fix instabilities and to tweak features so they meet their expectaions plus add more features they had expected in the first place - and to make all this come true in no time…
You may have a look at a similar product, e.g. X-Plane. First published in 1995 it has been under constant development since then, providing updates and new features several times a year. Looking into the forums you will find customers still complaining about bugs and wanted features - even after 25 years! Of course X-Plane is a much more mature product today than FS2020 but customers still are not satisfied.
I think it is realistic to give FS2020 a time of 2 or 3 years (at least) before most users will be happy with it. Until then X-Plane will be my every day flight sim and FS2020 will be tested once in a while for improved and better features.
Cheers!