or will they only be used by a small group of people(like now being used) ?
I think that Defi is one of the biggest inventions of the crypto space that has ever happened, together with Ethereum and the introduction of smart contracts, which made stuff like Defi, Dexes, yield farming and all the other stuff possible to begin with. With Defi you always have the full control over your funds because you are in control of the key of your wallet all the time. The only thing that can happen is that the project where you are having your yield farm is making a rug pull or is hacked or something. You don't have that kind of risk when you put your money in a traditional bank, that is also part of the truth.
I think that Defi nowadays is already used by hundred thousands of people so in my personal definition, that is not a small group of people, but of course it is also not the broad masses.