There are far too many cards for them all to be leagal and in tournaments with moxs and black loctus you can't be creative, you have to play the perfect deck and hope you go first.
I really think that those cards have gotten such a mystical rap that they're attributed to way more power than they actually had. I played in tourneys back when Magic was just starting to have tourneys, and they really weren't that significant. The problem is that every once in a great while, someone would get super luck and draw a couple mox and the black lotus in his initial hand and have sufficient other cards to be able to utilize the mana to do something nasty on the very first turn and everyone would be like "OMG! Did you see that!!!?". Then they'd conclude that it was unbeatable and unfair.
But they didn't make note of the 1000 other times the same cards were put into a deck in the same numbers and didn't result in a first turn boost like that.
It's really dumb. Limiting the card pool you can select from is actually what inspires creativity.
I always saw it the other way around. Creative is coming up with ways to win that aren't the stock methods that everyone talks about. One of the things I found is that the combinations that everyone talked about were super powerful on the rare occasion they worked perfectly, but were mostly just average (or even less than average) most of the time. The best decks were those which could do something useful and powerful every time. I remember a girl I knew who constructed a deck that seemed to win nearly every time. The odd thing is that there didn't seem to be *any* plan to it. There were no obvious card combinations within it. No overloading of certain types of cards to ensure a combination at all. Just a seemingly random jumble. You couldn't look at the cards and figure out why it won. It just did.
Now that was a Magic deck! And it required something well beyond creativity. ****. The thing was a kind of art. I'm more of a planned strategy player. I could never figure out that deck. But it worked. Go figure!