Reasonable likelihood having carryon weighed is my experience in Asia and NZ, and it is simply not worth the hassle of playing games around this. JetStar NZ actually gets all pax to line up and each carryon is weighed and tagged as ‘OK’ (or not).

As to whether or not 7kg is ridiculously low is oft discussed/debated - but I really don’t see the point. Either check your bags and/or fly with another carrier with a different limit if 7kg is bothersome. I am aware that US travellers (to generalise) seem to have a strange objection to checking luggage/bags….