If you want to farm reasonable airdrops I suggest that you stick to testnets, they might take time but your efforts won't be wasted.
I simply don't understand this part of your post. Why should someone farm testnet if he isn't a developer or something? Testnet is just a separate Blockchain for testing a new project. Or is there any other meaning to it I don't know of? Those telegram airdrops were fun while it lasted. A lot of persons made some really good amount of money just by taping or playing those games. There are still a couple of them but there aren't worth wasting your time on. Like you said, the best way to making money in crypto is by trading and holding. So I agree with that.
Coupled with the fact that testnet demands a high level of professionalism in crypto to carry out. Not everyone can run a testnet mining.
Talking about Airdrops, it's credibility was lost after series of listings that ended up as DUST.
I can remember telling my friends that Hamster may end up being one of the most successful projects in Airdrop era because they never requested anything from the community but paid the much they could.
Recently, almost every Airdrops now want you to invest. Even after investing, the listing price will still keep you at a lost. No one wants to loose, hence, I believe that Airdrop farming may tactically crash completely but it all depends on this January listings.