I agree. But to reinforce that separation, PMs ought to behave more like any other topic. They should appear in the Latest feed alongside all the other topics (but of course only visible to its respective invites).
There were discussions about how to approach this when PMs were first introduced. I think we concluded that treating PMs as something more separate from topics (with its own special feed interface) would ensure a more safe (privacy-protecting) implementation. While it was probably true then, it may not hold up today.
I know @joffreyjaffeux is also leaning towards making PMs behave more like regular topics.
Found one prior discussion related to this, but I feel there are important ones that I’m missing: