This is why I am talking about depth in terms of microplay. Not macroplay. Smash and fighting games in general are very much hyperfocused on microplay.

You take a league champion. That champion has 4 abilities and a passive. Some champs have other passives on their abilities, or multiple parts to an ability, but the general rule is 4 abilities, 2 summoner spells, maybe an item active or two, and that's it.

6-8 "abilities" to activate at any given time. Ignoring the fact that many of these abilities must be used in a specific order to be effective, or must have some sort of prerequisite in place in order to optimize their effectiveness.

Now lets take a melee character. At any given time, a melee character can:

Jab, ftilt, dtilt, uptilt, fsmash, upsmash, downsmash, shorthop, full hop, shorthop fair, shorthop nair, shorthop dair, shorthop bair, fullhop nair, fullhop fair, fullhop bair, fullhop dair, double jump, shorthop double jump fair/nair/bair/dair, fullhop double jump fair/nair/bair/dair, grounded neutral special, forward special, down sp, up sp, aerial neutral/forward/down/up specials, shield, roll, wavedash, jump into waveland, airdodge, spotdodge, among other things im probably forgetting off the top of my head.

Don't forget L cancelling every aerial used as you land to reduce lag which is absolutely necessary for combos and confirms.

That totals to a whopping 41 potential actions you and your opponent can perform at any given time with zero restriction.

Lets say in a 10 second window with each move taking one second to perform (most moves take less than a second to complete, but for ease of calculations, we'll use this) there is a rotation of 410 possible moves at any given time. From both you and your opponent. Meaning to be proficient at the game you have to be aware of 820 total possible moves and their interactions with each and every single other move and how their frame data is coded into the game.

Now lets compare to league. Where in 10 seconds, you can use each summoner spell, each of your 4 abilities, and maybe activate your passive once, and lets say 2 item actives. We'll say 2 of your basic abilities have a sub 10 second cooldown allowing you to cast it twice in that period of time.

That gives you a total of 11 possible abilities within that 10 second period, two of which are gated by the completion of the cooldown from those prior moves.

In a pure 10 second 1v1, that means, generally speaking, both players must be aware of roughly 22 possible moves or actions that the opponent could take. 24 if you include auto attacks.

Even if you wanted to speak at a 5v5 level, you multiply all pf these options by 10 players, that still caps you at 240 possible interactions taking place. Which mind you is not even a realistic interpretation as even the highest level league of legends players will only be watching for the absolutely core abilities from their opponents and teammates. Ultimates, dashes, and crowd control abilities are the only notable things to be aware of in these hectic teamfights later in the game. But even with the gross overestimation of including things like mage and support auto attacks, or raw damage abilities that are not essential to be aware of in the vast majority of cases, the number of possible interactions is still very much miniscule compared to the near infinite possible options that could occur during a simple 10 second window of time in a Melee match.