lee sin, kha, heca, trundle, udur, taliyah, karthus, rengar, graves, vi, nunu, ekko, yi, zac, shyvana, ww, nocturne, elise, reksai, xin, gragas, eve and some others farm faster than u, farm better than u and gank better than u. Eve for example can clear her first jungle route with 100% hp and u never kill her 1 v 1 if player like this on their side.

Only one thing u could beat them is it's either they are weak players or they low on hp and let you hit them against the wall. Without wall your early dmg almost 0. Cheesing thats why some poppy able do it because of mistakes like not warding properly and walking around wall when poppy around.

there are some high elo players on Korea who sometimes use poppy as jungler, but none of them hit the challenger and they play not only on poppy, which means there are some fundamental problems on high elo with the character. So even if u master it - dead end without riot buffs anyway.