I have somewhat more experience with QGIS. It has a standard Mac menu bar, but the icons are inelegant and Windows-ish, window layouts are Windows-ish, dialogs don't behave correctly in Mac full screen mode. It could use a MacOS glow-up.
I think Visual Studio Code (native menu bar, native save/open, but a core UI kind of unto itself that is consistent across Mac and Windows) does a better job of balancing cross-platform vs native.
And then there's the approach taken by Adobe and Microsoft Office. These apps do a much better job of adopting native platform appearance and conventions (sometimes at the expense of application consistency across platforms).
As for the common dialogs, I agree with you. There's no better example of why you should stick with common dialogs than the shitshow that is Microsoft Office. The file-save... thing is mind-bogglingly bad. It looks like a hastily-thrown-together debug screen. You have no idea what you're looking at. The fields are primitive, unnecessarily-huge box outlines. There's no treeview to show you where you're working in the filesystem. There's a big list of what, history? Why?
Garbage.