You may ask "Why only ES300h let my wife's M35X feel old but not GSF". That's because GSF is much more expensive. So of course GSF > M35X. However when I find ES300h steering feel is better than M35X, I suddenly realize M35X is old now.
I also finally confirm that my G35S is still good. (That's why I keep loving to drive my OLD G)
So the conclusion is :
"If you want to let your old car feel like REBORN, you may install some very good coilovers like KW, Ohlins, Bilstein to improve its performance to like new level. (but you also need to sacrifice some ride comfort... )"
I think it's not fair that I compare ES300h and M35X because M35X is almost 10 year old. I also think it's not fair that I compare GSF and G35S because G35S's ride is MUCH more stiff.
However one thing I'm pretty sure they all are excellent cars because GSF and ES300h will be like my OLD M35X and G35S and last VERY VERY VERY long time.