What is the infrastructure layer for blockchain development similar to - IaaS or PaaS or middleware, and how does QuickNode fit into that layer?

Let's just for a second back up and talk about Ethereum. 

Ethereum is a general compute that is distributed and it marries your state with your business logic. That means your database and your application code are together. It's kind of like if you took all three of those examples (IaaS, PaaS and Middleware) and you just smushed them together.

At the base layer, you need some set of infrastructure that's running this stuff, that's the RPC level where it's just whatever comes out of the box with the open source software clients. But the way that you access it isn't some VPS that you get to manage. The way that you access it is like a Twilio or a Plaid.

You need to call its API, but then, there are additional layers to it. The past sort of analogy comes into play where you have these indexes. So we have an ERC-20 index of every single token that exists on Ethereum, what the balance is, when, and all the transfers that happen. 

It’s the same for the NFTs. We have the most up-to-date owners. That's sort of abstracting away the complexities of raw infra and giving you more Web2-ish kind of calls. Then again, you're consuming everything through an API. It's hard to fit it into any single one of them.