The default theme makes it easier not to be original, but I don't see how it makes it harder to be original anywhere.
If it makes it easier for people to communicate faster, than I'm all for it.
I am sorry, I am not a designer and not a native English speaker, this makes it a bit harder to formulate this correctly.
Then why would you even be talking about Bootstrap, let alone criticizing it from a design point of view?
You can take any past, present or future "original" concept and build it with Bootstrap. You do understand that, right? You are not limited to the default theme. If you're lazy, lack talent or interest then yes, your website will look pretty much the same as those of your peers, but then you can only blame yourself, not a CSS framework.