Aphelios has a few problems.
1. His difficulty comes in for the wrong side
Aphelios is supposed to be difficult to play, but lets be real he isn't.
You read the primer a couple times to understand 80% of his kit, dink around in the practice tool for 10 minutes to figure out exactly how Chakrams work, and you've basically got the gist of what he does.
If you go into a game as Aphy understanding how his kit works and what the abilities do, as long as you've got a solid baseline as an ADC player, you're going to be fine. His kit conveluted, but not too complicated when you're playing him. It's super intuitive.
There's some level of strategy to burning through your guns to get your preferred combos, but lets be real you can just go with the flow for the most part.
The champion takes no more mechanical skill than any other ADC, since he's remarkably intuitive, but knowing what the fuck an enemy Aphy is doing is difficult.
2. None of his weapons have enough flavor individually
Individually, each and every one of Aphy's weapons is a great design.
If you threw them onto an individual champion and built a kit around them, they'd be great, but since you've underdeveloped each one and thrown them into the same kit, the champion is just crowded.
Each of those weapons could be developed into a full kit, but they've been cut down to the point where nothing works.
3. Moonlight Vigil just fucking sucks
I'm not saying it's weak, because it definitely isn't. We've all seen the clips of Firebombs instantly pentakilling clumped groups of squishies.
It's a potentially strong spell, but it's the most boring ult we've seen added in years.
Morello: "Ok so Morde takes people to the Shadow Realm for a fight to the death, Senna shoots a beam of light and shadow across the map, and that Punchy guy we're working on has a suplex. What's Aphelios going to have?"
CertainlyT, with a hangover: "Uhhh, yeah man. He throws a bomb and then shoots the guy."
It's clunky, bland, and honestly doesn't fit very well into the champion's gameplay.
It feels like you just ran out of time with this spell and just phoned it in.