The airdrop of the Hydro was a real gold mine, because the reward was pretty good.
The examples you mentioned were some happy cases, but in 2019 airdrops are a waste of time.
Why? Because to get a project to receive the airdrop reward, you have to attend another 10,000 airdrops, and that's a waste of time.
The time spent to create the airdrop, you can consume it on bounty campaigns. I no longer participate in airdrops.