I think it depends on where you are from. I'll share a bit of my experience from India:
It seems kind of pointless to combine just a bunch of stock images
I don't think so. It is certainly more than that. I know things like this happen in my small agencies or startups, but most of the time you'll be asked like:
create something unique, don't ...
There are some Graphic Design jobs where the focus is mainly social media content but you might also be tasked with doing web banners and email campaigns as well, I personally have not held this kind of role, but I have interviewed some people with this as their job.
A lot of the time, people will design a graphic that isn't just a photo. Just like a web ad, ...