Did you even play her?, she is hard to master, her combos can only land through her elements which are highly situational, she has no sustains, no heals, no shields, she has a weak wave-clear, her ult is tricky to land as it deals no damage if it doesn't proc against an element, and to top it off her E travels a fixed distance which if you don't know what you're doing you can easily overshoot yourself to an enemy tower or into other sticky situations, there is also a bug with her W on bushes in jungle camps as it sometimes reset the camp due to lack of vision from the camp on her, she's one of the slowest jungle clearers early game, so if you don't plan and execute your route perfectly you WILL fall off in levels (the new patch that nerfed jungle exp made this even worst) a big part of this plan is highly dependent on your teammates to not beg for a gank in the first 5 minutes or every 30 seconds, if you go 1/3, you have a higher chance to win the lottery than to make a comeback as her damage goes down the drain without her core items
Fun fact: she is an AD assassin, every assassin requires mobility and at least one form of stealth or a disengage since they tend to be squishy, so I don't really know what are you complaining about here, you're literally complaining about an assassin that has an assassin's kit, and not the easiest one at that too, many champions do it better and many counters her, you have diana, you have leblanc, you have neeko, and basically every bruiser in game can out-damage her