Strongly disagree. The obvious counterexample is in the foss world is ffmpeg, which I would submit is deeply understood by Fabrice Bellard. As a sibling points out, there are also various worthwhile single author projects.

Outside the world of foss there are for example multiple games that are highly respected that were all entirely or largely developed by a single developer. Rimworld, Songs of Syx, Dwarf Fortress, Ostranauts and many others. In a proprietary context I have myself deeply understood codebases and worked with others who have also.

That being said, you are arguing against a straw man that neither I nor the rust article propose. They are not saying maintainers need to understand all the code they are saying the person submitting a pr needs to deeply understand that pr. Why? Because they want to build a community who deeply understand various aspects of rust so when things need maintenance there are experts around who even if they don’t know a particular piece are invested in the success of the project and know enough to get up the curve and fix whatever needs to be fixed.