It also overlooks that China has historically been conquered by outside forces as its leadership grew weak. And the Communist party was having enough trouble internally feeding its people and causing issues like the “break four olds” period that there was little ability to wage effective war.
Let’s also not forget the the communists literally aided the Japanese in the rape of Nanking as it helped to undermine the GuoMinDang.
The proton client for Linux has improved recently. I use it on PopOS. As to your first point I agree. I landed with Proton specifically because it was cheaper to do it and email rather than separate services.