I'd be tempted to go along with that had Brown's FG% not nose-dived last season. But in fact he shot a career worst, under 41%, compared to his lifetime average of 46%. His free-throw shooting also slipped, fading below 80% for the first time since 2000. To me, that looks like someone who is running out of gas.
Thomas had puzzling problems staying healthy in Phoenix, but before coming to the Suns, his track record for health was every bit as good as Brown's. (Thomas and Brown each missed a total of 12 games in the six years from 1999 to 2005.) His per-minute production held steady, right around what he did with the Knicks over the previous several years. If the running "system" was too much for Thomas, who was only 33 at the start of the '05-'06 season, I don't think I'd expect the 38-year-old Brown to fare any better.
Bottom line: Brown right now looks like the Thomas of 2005, except that he's five years older and his numbers are already starting to fall off. The idea that the Suns can plug Brown in to Thomas's spot and not miss a beat is fantasy. And that's if they even get him at all.