IDK, you can be in the mid game and see what people are building, and try to counter it/build against it
Let's say someone's building rangers and they're at 3 different rangers, and they're absolutely steaming everyone. So the natural response is to go assassins to kill their rangers before they can whittle down whatever team you have?
So what do you do when the game throws 3 giants belt and a chain vest at you? Where is the skill? How do you account for this?
The only consistent strat I've seen is the reroll strat, and that can go tits up or be unstoppable depending on what the game starts throwing at you. You can either get a bunch of random 3stars with no synnergy or you can get a team comp if the game is generous, and there is literally almost no outplaying the raw numbers of 5+ 3 stars.
If it threw three items at you every mob round, and you'd only get to pick one, then you'd at least stand a chance of relying on your skill/knowledge of items/matchups to win.
Imagine getting random items on summoner's rift? It's so frustrating.
Maybe also give a chance to manually ascend a character, and it costs double the amount of gold per copy to do it but there's no RNG factor.
Then the game would be more about economy management than complete RNG.
As it stands right now I'd say the game is 80% luck, and 20% skill. There's just no consistency.
I want to say you have more control of your games in ARAM, and that's saying something.
Some After Thoughts: Managing the economy would now be a lot more important. Knights are extremely cheap, so you might go a knight comp with a frozen heart vs rangers, because now you know how to build one, and you know you need to get through two rounds to get the items you need to build one.
Also another thought on the manual ascension. Now gold is guaranteed power, and you have to weigh how to get gold. You have to weigh interest gold vs win streak gold. You have to spend gold to gain temporary power to increase win streak gold, vs not spending money and gaining interest gold.
This is how you make it a game of skill.