I think it is impossible to be a millionaire now just by doing airdrops. Airdrops today cost nothing or if you are lucky just $5. The highest I got so far from an airdrop is $6. Bounty millionaire is possible but for airdrop only it is not.
It's even impossible to earn a few dollars from the airdrop. The golden year of airdrop already passed and it will never comeback again. I have participated in the raiblock airdrop and i have made more than 500k dollars from there through sold all of my NANO and it's called raiblock in the past.
It's possible to be a millionaire from airdrop in the past but that golden year will never comeback again.