It's probably the best of its kind (mmo), but the number of players is constantly (slowly) decreasing. Mostly from players getting too old or dieing. Alternatives: Warbirds has even lower numbers. I'm not sure about the current state of the war in the air in WW2-Online.

Can an open source game of this kind find players? Probably not many, but possibly dedicated ones. The problem with that target group is that someone will reference the charts from the POH or from published test flight data and complain that the simulation does not match the numbers.

I wonder if Aces High 3 works well on LINUX thru an emulator like WINE. And I wonder if you'd need a monster computer to get a smooth frame rate through emulation like that.

LAC, BTW runs very very nicely on cheap laptops and even does pretty well on Raspberry Pi 4b.