The simplest conclusion is that martingale gives you a bit of profit in the beginning and the more you have in the bank the harder it is for you to fail and lose everything.
Gambling is based on luck and there is no guarantee that you will win even at the beginning.
Don't start with low bank or you'll have no chance to earn profit but if you are willing to risk a lot of money it's not the worst strategy but it always makes you lose in the end.
Higher balance and a low initial bet amount causes you to have to repeat the martingale method more times. However that causes the number of consecutive lose before failing decreases, it causes you to have a lower chance of winning.
For the Martingale strategy, you really need to have a big bankroll so that you have the balance to double your investment with every lose and if you run out of balance, you will eventually lose all.
How much money do you think is needed? Are 21 millions bitcoins enough?
As you yourself said you will eventually lose all. But note that it will finally happen even of you have all 21 millions bitcoins.
Rather than focus on strategies like martingale etc it is better we focus on money management techniques. If we understand how to manage the money and how much to spend every day / every week in gambling, we may not lose much and at the same time gambling will be pleasant and fun for us.
Yes, you can manage your money to not gamble more than you can afford. This only decreases the amount you less if you can overcome greed. But money management cannot overcome the house. The house give your money. Does not matter it's a big money or only a few cents.