The jungle update doesn't really make assassins level up faster. There is really why it was called hypermeta carry meta back then bc assassins will be lv. 4 faster than right now. Why, simply, the first wave gives lv and they get more gold to funnel in hyper carry model.
I think it's balanced by the jungle item that nerf minions gold coins. Assasins could also be trash/useless when you 're harrasing them in early game, esp, their blue buff (for ling , fanny, lance, haya). even they have more exp/lvl, doesn't mean they have core items like demon hunter sword or Blade of despair. Try using hilda , jawhead to harras their blue buff .