It's true that the best cards are in high demand and it can take a couple hundred dollars to create a deck that's the flavour of the month. However, simply having such a deck is no substitute for the skill that is required to know how the deck works, how it matches up with the other decks in the metagame, what your sideboard should be, when to sideboard, counting cards, all of that jazz. There's still a ton of skill involved, and while money is a big aspect of unlocking your abillity to do your best, it's like saying Nascar is play to win because your Average Joe doesn't have the money laying around to buy himself a racecar. Not to mention there are other competitive ways of playing Magic that aren't as gated by money, like Sealed and Draft, these limited formats are great for adding to your card pool without the waste of just ripping open booster packs.