"One source estimated the spreadsheet found upward of 90 percent of the dossier’s claims to be either wrong, nonverifiable or open-source intelligence found with a Google search."
First, that means that about 10% of it was correct. Maybe that's a poor percentage, but it's not zero.
Second, the 90% includes "could not be verified," which means maybe it's true, maybe it isn't.
Third, the 90% includes true things which are discounted because they can easily be found with Google. In other words, they're true, but Steele doesn't get any points because they were easy to find.
Does this put a stake through the heart of Steele's claim. Maybe, but if so, I am actually not even sure what the heart of the claim even is. All I can say is that it is not technically true to say the the dossier was completely fake. It was never considered absolutely reliable. It was only considered credible. Beyond that, I don't have a stake in the outcome of the argument.