How do I know if I possess the potential required to be good at Smash? Like, which skills do I need to clearly demonstrate in my play, and how fast does my growth have to be in order to show that I DO possess potential?
This is a very vague question in a sense. In order to be good at smash you need to have some physical capability, (and even then, there are those who do very well with a lot less physical mechanical ability) that would with a combination of other factors result in
good play, skills like thinking, (for decision making, judgements and adaptation, reading habits, awareness) knowledge and determination to keep playing.
What is 'good' to you? Top 60% of the playerbase? 30%? 1%? We could quantify, and I don't mean to sound terse or subjective, or nit picky, but this is a pivotal part of your question because your talent and time being spent towards this end relates to the answer, if you mean to ask if you have the talent to, say, within a year be on the caliber of top 10, that's a different territory and question than "could I be good enough to beat most non-competitive smashers?" This requires an answer from you.
How do you know? Well, you'd have to have a truthful understanding of the skill of smash and your own skill and potential, and how do you know that without being committed for at least a little while before? How do we know? We don't, and you probably don't either. It'd be convenient in a lot of ways if we had a very accurate
skill-meter to measure anyone's talent along with potential, how long it'd take them, on any given activity, but we don't. But that's essentially what you're asking. Your growth doesn't have to be fast, but if someone is talented usually they'd have a lot faster growth.
I do believe talent exists, and I do think the evidence strongly supports that, but people are also generally talented, so we tend to have a gift for being good at multiple things if only we would put our time and effort towards it. In a more technical, literal sense we may say truthfully that everyone must have some smidgen of talent to use or do anything in that one thing. But not all talent is the same, some are more talented than others. How would we know that with a glance or without knowing anything? I'm sure in history, there have been those that have had immense talents, but never went into their talented field or work, and also those that didn't particularly like what they were talented in.
But does that still mean I have a big disadvantage compared to other people?
It could, but we don't know what your '
talent' is and it's also compulsory to ask the compounding question; does it
matter? How much does it matter? Should it matter? Do you have fun playing this game? Is your objective in this game or activity to have fun, or simply win? Is it both? To what extent? Suppose hypothetically we knew you were less talented and at a big disadvantage compared to others, if so, what then?
People have all sorts of talents and traits. Some have better reaction times, speed, better eyesight, better hand-eye coordination, endurance, whatever the case might be. I'll quote Qui Gon in the last Jedi "There's always a bigger fish."