Mining, when it could still be done with graphics cards and early mining machines.
Gambling, the early sites SatoshiDice and later Just-Dice had huge followings. Looks like there is still a lot of crypto gambling just split up over many more sites now.
The early Altcoins such as Dogecoin and Huntercoin.
Tokens and Dapps made possible with Ethereum.
Earlier Tokens with the airdrops were very profitable.
Dapps looked very promising at first, not sure they've lived up to it yet.
Something you've missed in your list which has been there since ever. It's HODL.
Holding bitcoin or other cryptocurrencies you think it's really valuable for a medium to long periods would generate the profit you dream about .
Those who bought to hodl btc before December 2017 are actually financially satisfied.
Gambling, mining, and alts are all for fast profit and are all somehow a sort of gambling as you predicted that the method is profitable, when for btc if you think it's the currency of the future than you would never lose; at least for the next decade .