I don't really know much about how YC funding works, but some of the startups listed on there are for simple things like browser extensions, which surprises me.
Browser extensions can start out as very simple but quickly turn into very complex pieces of software. Have a look at postman(https://www.getpostman.com/) for example.
It's a fallacy to think that just because a product is a browser extension it must be very low-tech easily-imitable app. I know there are some browser plugins that are quite sophisticated and have a complex programs in the backend. For example: Ad-blocker, LastPass, etc.