If you buy a bitcoin in the price of 9000$, yes it may drop, but we have clearly seen that this is what it does. It goes up and down. If you have 1 million dollars and buy 100BTC (900.000$) then the only thing you have to do is wait. Because someday it will pass that number and you will have profit. Am I wrong?
The more bitcoins you have in your account, the more naturally you can earn. But do not forget about the fact that the prices can not only rise but also fall very quickly. Specifically if we take your example that investing a million dollars in bitcoin should be expected in any case only to increase your income. Bitcoin was able to please many people and ruined many. This should be taken into account when investing. Personally, I try to buy a little bit of bitcoin every month, regardless of its price.