First Street very likely doesn't have some magic model that can predict the future better than anyone else.
When you get a mortgage you have to pay for a flood survey. Even my house 700' above the village where the bank is.
Your flood risk is absolutely predicted by the flood history of your location. The bank writing the mortgage has the skin in the game which is why they make the buyer pay for the flood survey.
It sounds like First Street might be liable for damages based on pseudoscience if these Realtors bring a case. It would be interesting to see them present solid evidence that they prospectively beat the existing flood models and survive a cross-examination.
If they've published a peer-reviewed paper then I missed it.