There is however a difference between a retarded Jax initiating every fight by jumping into your team, and a Nasus who can't just jump into your team; besides, Nasus' job isn't to rush enemy carries, he's just supposed to Wither them and then kill whatever's in line of sight, a good Nasus, that is. You can't just be all "herp we'll just zerg him down (please, it's a fucking nasus with 4-5 major defensive items, plus an ultimate and lifesteal) and then disengage"; you say that when you've zerged ssomeone like Karthus down or a bruiser (LIKE JAX) who're fairly easy to instagib and if you're behind, or you don't have the composition to teamfight and you rely solely on catching someone off guard, then taking the win and backing out.
If we're asuming we, ourselves, are good, can we atleast assume our opponents have a couple braincells aswell? As if any self-respecting Jax player is ever just going to jump into your team without a care outside of soloqueue or low-tiers of team ranked.