That's not true!
You'll end up with more bitcoin almost every time if you market buy ASAP. Mining will acquire bitcoin at a delay and it will usually be less than a market buy at spot price at the same time you would have bought mining equipment.
Even in the very early days. You could have used minimal power to mine 50 BTC 2 or 3 times a day! However, if you found a seller, you could have acquired thousands of bitcoin for hundreds of USD!