You wrote visual editor is the default editing experience on desktop, and that desktop, brand-new editors are mostly using visual editing. This is incorrect. Our wikis are fragmented into four configurations:
- For the largest group of editors, wikitext is the default editor.
- The second largest group do not have a default editor, the wiki default provides parallel links to both editors.
- The smallest group is... I think two small wikis ...where VE is legitimately VE-primary.
By the way, the "alarmingly low" wikitext completion rates and higher VE rates on mobile are obviously because all of the worthless curiosity-clicks get dropped into the default editor. Approximately no one gets into the VE-bin unless they're an experienced editor deliberately swapping to VE. The desktop completion rates are also junk figures, dominated by the fact that a random percentage of wikis drop users into different defaults. Non-default usage is almost 100% experienced editors, with obviously higher completion rates.