Im not with u on this one.
I was told when i was talking with someone in chat box to do it in pm.
If u take it to pm in chatbox and relog or disconnect or w.e all pm's dissapear (from chat box).
If u use forum pm u need to refresh all the time otherwise u wont notice if someone send u a pm (or there is an option for automatic notification that im not aware about).
So yes discord and skype can be used by imposters and osbot cant but the use of discord or skype is in my eyes way more user friendly (like i mentioned above) than osbot.
Both got ups and downs.
My way to avoid discord imposters is to have a talk with them on discord and pm eachother on osbot to make sure its the person ur talking with.