The MacBook already has mediocre battery life, and its case is pretty much solid battery except for the tiny logic board.
So ASUS comes along, shrinks the case and puts in bigger and more power hungry CPU / RAM / SSD plus extra components like the mini CPU fan and Thunderbolt controller. Guess what's gonna give?
It sounds like the original MacBook Air; great on paper but in reality a bunch of overpowered components packed in too little space, leading to crappy battery life, overheating and throttling.
I realize everyone wants ultra-mobile devices these days, but if you're tethered to a charger it's not so mobile anymore, is it?