The problem here is that unless you are an Akali spamming Qs or a Kennen using E with half of the energy bar, it's really difficult to run out of energy in any champion. They have more than enough for one rotation of their ablilties, and by the time their abilities are off CD, they already have almost all of their energy back. The only thing energy does for most champs that use it is preventing them from building a lot of CDR early on to have their important abilities quickly off CD in lane. Zed rushing CDR early on to have the shuriken on a 3.6s CD and the shadow on a 13.2s CD would be a fucking nightmare.
I almost never see one of these champs running out. For most of them, you could increase a bit their cooldowns and remove the energy mechanic, and that would be it. Keep in mind that I said most of them, energy is the only thing that keeps Akali from spamming 1Q every second.
Ironically, the best energy-like system in League is not in an energy champion, but in
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You actually are able to burn out your resource bar without having to spam 3 rotations in a row, so you actually have to be careful.
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You get aditional benefits for keeping the resource bar on a delimited zone. That alone adds a lot of depth to that mechanic, and rewards resource management.