Actually there are a couple of tests that we could perform but much of it you can simply observe on the ladder. E.g. most people at rank ~10 and on wards have a big enough card collections to put together at least one or two good, meta decks. That is; build a consistent deck, with high quality cards, and one that performs well on the current meta.
In other words, even without a full collection, the decks they play are complete and the only thing they are missing is the skill to progress, whether to rank 5 or further to legend, doesn't even matter which.
Another tangible test you could perform is take a highly skilled player, give him an inferior collection of cards, and then pit him against inferior players with superior collections. I guarantee you the more skilled player will win majority of the time.
It is about reading the meta, taking advantage of it, how to counter it, deck building, understanding value, how to trade, how to balance, build a curve, how to mulligan, play around your opponent's deck, and so on. These are all things that new and inexperienced players need to learn and just by doing so they will improve their play immeasurably. If anything, getting enough cards for one functional deck is the easy part.
A compelling argument would be a good start. Perhaps some observable facts maybe. So far you've produced none and talking about ignoring everything people say, you've been pretty good at that yourself. It's the pot calling the kettle black.
For one thing, that applies to you as much as it applies to me, and secondly, it's a load of shite. It is essentially you say, "I can't win a rational argument so I'll just argue he's irrational."
Here's an advice for winning arguments that I'll gladly provide; attack the argument, not the person. Starting to make up stuff about me will get you nowhere.