haven’t tried one, but I’d bet that NASA didn’t put the foam in the seats to absorb the G’s, as they only last a few minutes. More likely it’s to make the seats more comfortable when they spend several hours on the pad lying on the seats waiting for launch.
A friend of mine has done 5 flights, and she’s normally the 2nd person in the orbiter after the commander, she’s spent 4 or 5 hours at a stretch in her seat before launch.
J.