Not sure about “less jet lag”, but I definitely sleep better in 787, and feel better.
I have done a number of Europe-SIN flights on SQ 350, SIN/MEL-West Coast and other transpacific/transatlantic flights on UA 787 and Tokyo-Europe flights on NH 787. Overall, I feel better and sleep longer on 787.
The reason I don’t sleep better on SQ 350 is because its business class seat is so hard in flat position, it is hard to sleep despite better air cabin pressure.