I remember unpacking obsidian.asar to inspect the MathJax inside. It’s less than 2MB so it cannot be a full MathJax. More powerful MathJax implementation is usually an order of magnitude larger in size.
Auto-numbering aside, Obsidian struggles with complex equations in general. For strange reasons, I get the unrendered display equations with yellow background after a couple of previews of math documents, even though the initial preview is fine. The only way out of it is a relaunch. It’s so exacerbating that I stopped using Obsidian to process any document with display equations.