As I've said countless times...any art can be effective, but it all comes down to how it's trained. Can BJJ be useful? Of course. But like everything, assess each situation and act accordingly. To intentionally go to the ground...well, that's foolish, IMO, but thats just me.
The portion of the quote that I've bolded is the important thing to remember.
Speaking as someone with a brown belt in BJJ and almost a decade of serious training in the art, deliberately choosing to go to the ground in a fight would not be my first choice in most circumstances. That said, there are circumstances where it might be the best choice. In other circumstances, I might not get to choose where the fight goes.
Ideally what you want is
a) the ability to quickly assess the situation and determine the best option (fight standing, fight on the ground, run away, etc)
b) the ability to take the fight where you want it to go (get the takedown if you want to fight on the ground, prevent the takedown if you want to fight standing, create distance if you want to run, etc)
c) the ability to defend yourself standing or on the ground if the fight doesn't go where you want it to
Hopefully we can all agree on that much at least.