I don't think bounties will be considered "free" because most of the bounties need some work, you need to complete some task before they reward you also with airdrops, some of the airdrops became bounties like you need to follow their instruction or task to be rewarded.
What airdrop really is, you just need to give your wallet address, or no need anymore, they just do a snapshot for all the wallet addresses on the network based on them.