Yields at the moment are crushed, but during the hayday you could make insane money.
Almost all crypto trading firms have some sort of defi yield farming presence, and many tradfi firms were thinking about entering the space. Whether they still will and if yields will recover is still an open question.
There are definitely some dapps that are pretty solid imo: uniswap, aave, maker, curve, and alchemix to name a few.
Whether it's all a scam is a good question, but from my perspective it doesn't really matter. The goal is to make money by being smarter than everyone else.
I don't think I'm making the world a better place or really helping anyone besides myself/firm, but that's okay.
Some people think finance is perverse because it attracts tons of top talent and utilizes their skills for a dubious purpose. While this may be true, it's also true of many other industries as well: most notably, big tech. Ultimately, people rarely make employment decisions by thinking of how many people they can help.