Yeah, they scale up the amount you would receive in terms of $ worth, no fixed amount of token/coin so the paying is kinda low with only a couple bucks per week. All the good-paying bounties and airdrops are full or limited. Thought I think bounties and airdrops are still worth as long you can join in the good-paying or cherry pick a really promising one to join in.
Yes, it's obvious because every good choice will always pay very well for the duration of time we give and the payout will also be adjusted, so there's nothing wrong with bounties and Airdrops so far, because good proof of payments is still in some projects.