For a while I was building only websites, but eventually took on web app projects that leveraged MVC frameworks and had to build upon in-house REST APIs that to integrate with the products.

No algorithmic problems, though, you're right about that. The closest thing I can think of relating to time complexity for web dev are when N+1 queries are used unnecessarily. I fix those, and change them into single queries.

For what it's worth, though, Amazon did reach out to me and I did two rounds of interviews with them. I bombed the tech on the second one.

Senior level web? Heh, even in web don't even think I'm that far. I have zero professional experience with anything but PHP which is going out of demand in newer positions.

On the JavaScript side I have done two React projects, all the companies I worked for had old-school JS though. Bunch of vanilla JS with jQUery strewn in, hundreds of files, no usage of Node nor modules.