When I bought my 2011 GS350 last summer, I was thinking the same thing. The bottom line is that you just can't expect too much cooling to happen in the GS350's seat's. After reading every thread on this forum, best I can tell is IF you can set your air conditioning temperature as low as you can, maximum air flow setting on bi-level, then MAYBE you are going to realize increased air flow into your seat, but don't count on it. Lexus assumes that your seat really doesn't need maximum cooling unless you are running your air conditioning as strong as you have to. I have played with every setting imaginable and it is frustrating. I have considered taking out the seats and replacing the fans, but alas, it would be in vain unless you rig up something a lot more powerful than already exists. The only way you're going to get beyond this is just to lower your expectations for seat cooling and go on.

 

They are fan driven ventilated seats, and they aren't using the Pelitier effect to cool them down. Honestly, they are better than nothing, but you aren't getting cold from them.
The seat heaters aren't much to write home about either.
Seat heaters that go thru thick foam will never be as effective as the elements placed directly under the leather. Unfortunately they don't do that anymore because of Lawsuits.

Older cars had wires woven and taped to the back of the leather skins. Bad part is with all the flexing the thin(very high AWG wire) would create a low resistance point and just burn thru and either hurt someone or need to be replaced.
Now you are heating thru essentially thick insulation with a weaker carbon fiber pad.