My sienna Le is just as bad, but dealer said it was normal

I have a same model Sienna and an Avalon(  poorman's version of your GS300 ::). When I first got my Sienna, I had the exact same feeling as you now. It was totally different from any cars I had onwed. It needed much longer distance to brake. As a matter of fact, it was so bad, it made me  feel unsafe. And I had to take it to a local dealer to have it checked. The dealer said it was normal for Siennas. They also said the newer brakes were kind of all like that--felt softer than prevous models. (I didn't believe them, but couldn't do anything.) ... Anyway, they could do nothing about it. Now I've got used to it..and it feels fine now..Just my 2 cents.