It for sure is more complicated than adding files to a git repo. You are 100% right and I wouldn't dispute that for even a second. I'm not exactly advocating this for solo-projects unless you are already sure you want to do something like internationalize your project.

There are many problems where plain-text falls apart for even engineers though or there's some benefit to editing something through a UI or WYSIWYG rather than plain-text. If you're cool with markdown and editing SVG files manually -- do it.

The problem being addressed is when you have team members who need to do things that requires some level of type-safety but they either don't have the technical background to work with something like git or it would be non-sensical to resolve the conflicts in plain-text. The idea here is for designers to basically take control of things like icons and theming and for translators to take control of i18n. Their work is state that can be used to generate a type-safe API for engineers to consume those assets.