This is exactly right.
The FBI already knew, for instance, that Papadopolous had spilled the beans while drunk -- to someone he barely knew -- that the Russians had stolen emails in their possession. It literally started the FBI investigation. But to Trump's defenders, we're expected to believe that even though Papadopolous blabbed like that, he never communicated this to the people he worked with on the Trump campaign. Right...
Meanwhile, in exchange for his plea deal, Papadopolous gave additional useful info Mueller's team that none of us know yet. We can be sure it wasn't about the 13 Russians just indicted, though. Someone (or someones) else in the campaign knew all about the Russian thefts and hasn't gone public about it. I suspect we'll find out why.