Yes, the deal is for truthful testimony, just like it is with all witnesses who flip, and truthful testimony must therefore be damaging to Trump, because otherwise the prosecution wouldn't be making deals with these witnesses to testify to begin with. I don't think I can put it any more simply than that. The prosecution is not on Trump's side. They are not trying to help him. If they're asking people to testify and making deals with them to that effect, it's because their testimony will hurt Trump. That's how this works. That's how it's always worked. You're quibbling about a distinction without a difference.