You are equating crypto with payment but it's really moved on from that. The blockchain space really about competing with Ethereum to provide a decentralised platform for applications - what some people term as web3.
I was not aware web 3.0 is a thing yet. Is there any "killer" web 3.0 app? From what I've seen most are small crypto currency apps or web 2.0 apps with a crypto payment/token component. Is IPFS considered Web 3.0 as well?
Yes, I would say ipfs is an important component of web3. Ethereum has it's own competitor to ipfs called swarm which provides the static content hosting to pair with decentralised database (Ethereum blockchain), and decentralised messaging (whisper), to provide a fully decentralised application platform.
I'm not sure how a decentralized message application can be safe from flooding.
The biggest killer web 3.0 dapp right now is something generally refered to as DeFi (Decentrilized Finance). There are several dapps that make up defi, including MakerDAO, Compound, Uniswap, Dharma, dydx to name a few.