As per the other person's comment, yeah basically I could have broken it up but it would've been an arbitrary demarcation. I just deleted our functions and fixed everything that yelled. Admittedly that could've been one and then leveraging the libraries better could've been another, but they would've been 2 PRs that changed almost every line. So done as one to mitigate review time.
Why not leave your functions but have them invoke the libraries instead?
Arbitrary demarcations can still be valuable! Just because something is arbitrary doesn't mean that it's not helpful. Working in chunks will let you take more time to review each callsite individually, and increase your confidence in the changes
In the future, I would definitely encourage you to explore a more iterative solution—fix the first 50 occurrences first, or maybe all the occurrences of a handful of functions. For example, if you have utility functions A, B, C and D, maybe fix functions A and B first, and then C and D second.
Ultimately, at the end of the day it's going to depend on how much code you're touching. If you're only touching 100 library calls, then it's probably easy to do them in one PR. But if you're updating 1000 library calls, you'll need to take a more iterative approach. Building those skills now will serve you well in the future when working on bigger codebases and harder refactors.