Besides, canon is compatible with L39 and S mount(3 inner lugs), not R mount(3 outer lugs).
The mount(卡口) decides everything. The difference between SLR and rangefinder is not just 取景方式. They are in totally different design concepts. So that's why they have different mounts.
And make sure you use the quotes from official documents.
OK I see your point, you call all the mounts with a bayonet(卡口) a "R卡口"
But I just want to point out, 0.95 has a bayonet but it is called S mount, it is different from Canon R mount.
FD FL also have bayonets. Also Leica R is different from Canon R, so I don't call all the all the mounts with bayonets "R卡口".
So different company uses different names even though they have bayonets. You can't just use R卡口 this term to present "mounts with bayonets", that will surely lead misunderstandings.