It's unlikely that they'll actually use Git, but teaching them Markdown is absolutely doable. And any modern Git forge will let you edit a Git-based wiki in the web UI without knowing what a commit is.
"I want to insert an image." Whoops, you're already in deep trouble. "I want to resize it." Even worse!
These are table stakes features that everyone expects to work out of the box. If you don't give them a WSIWYG editor that does all of this for you automatically, it's DOA.
You don't need WYSIWYG for dragging and dropping images into a document, or even for resizing them. WYSIWYG is an approach to layout and formatting, not the only alternative to writing LaTeX in a terminal-bound text editor.
You are probably arguing with another developer here. Imagine having this same discussion with some business person who uses MS Excel and Word all the time, and trying to convince them that your text only thing where you can't easily add a chart coming from Excel is better than what they are currently using.
