Which ones specifically do you disagree about? I could understand saying something similar to
@Micah Sweet re: overall viewpoint but I cannot immediately/easily see any logical basis for even attempting to argue most of the games are lighter. Perhaps I've overlooked something? There are 2-3 I could see being potentially arguable as close to 5E, but I wonder if it's those you're thinking of.
Re: light/medium/heavy my definition is similar to the one others seem to be using (albeit you can have a different starting point, again cf
@Micah Sweet but the basis of judgement remains broadly the same). Specifically the amount and complexity of "main" rules you have to understand to play/run the game RAW is the the main factor, with exception-based rules also playing in (albeit obviously weighted much lighter, though some exception-based rules do need to be understood even by people not subject to them). Inconsistency and quirky-ness of rules, as well as rules being counter-intuitive would to my mind also make a game heavier.