The game is too complicated.
I was reading through an old post in which a slew of people tried to explain Lethality and League's damage calculations to eachother, back when it was a new thing. It was that post that made me realize League's glaring weakness, and the reason balancing the game is like walking a tightrope carrying a 20-foot stack of steel scrap in a driving wind.
The game is too damn complicated.
All the good MOBAs on the market seem to have fairly simple calculations. What you see is largely what you get. It makes balance tweaks much simpler when there are only three or four elements to the overall formula. League has gone wild, implementing like eight different formulae, each with 3-6 contributing variables and coefficients. It's sheer chaos, and I suggest the next big revamp be used to throw it all out and start anew with something a little simpler to grasp.
The players will thank you for making their task more streamlined, and your balance team will thank you for the same reason.