Professional programmer, working in the video games industry since 2012
I think it's worth noting that it's a common practice, when handling 3D models and other heavy game assets, to write a standalone program to convert some model interchange format like FBX, Collada, glTF, etc. into a customized internal data format which is then loaded and used by the game. In that case, even if the standalone program depends on a library, you don't necessarily have to integrate it with the game's build system or ship it to end-users.
A budding game developer and programmer
Also, things that only run at startup are still very much worth optimizing, sometimes early in the development cycle. Long startup times are annoying and, more importantly, increase the time it takes for you as a developer to iterate on the program.