Not true. I walked into Judo with no background, practiced for about 8 months, then entered my first tournament as a judo white belt with a BJJ purple belt and placed second in the black belt division...
I would expect you to do well walking into a Judo dojo, Kevin, because we already know you are an exceptional martial artist. (Am I correct in recalling that your background is in MACP?) But in this thread we are actually asked to make generalizations about a category of martial artists. For the record, I was coming out for BJJ players and stating that they can be extremely dangerous. I roll with friends who can tap me 3 times in 5 minutes. So obviously, it makes sense to take some prior consideration and appropriate training (which is why I still roll with them).
To do that, we're required to discuss the relative weaknesses in general terms. My statement about BJJ'ers not liking to get hit is based on their UFC performance (yes, my favorite yardstick again). Demian Maia is one of the few really successful "pure" BJJ practitioners (well, maybe Fabricio Verdum and the Nogueira bros. too). And I was thinking of Maia when I said that. He hates it. Top trainers have learned how to counter BJJ, so it's lost the exclusive dominance it once had.
A BJJ player needs to take you down to work their game. Judoka are specialists in take down defense. That is why I say "all other things being equal" the BJJ player will struggle to implement their plan. Once it arrives on the ground, the balance of power shifts, so how do they regain an advantage? This seems to be the original question.
I know you are a Brazilian Ju Jitsu proponent, so it's natural to take it's criticism personally, but I will still encourage you not to. I'm not making any personal judgements. Just answering the OP, which is about how to neutralize "a" BJJ attacker. We assume they meant no one in particular.