> Overall I agree with you, yeah. But also no. Of course the code should be as simple to understand as possible, but if the junior or medior doesn't understand matrices, nothing I do will make them understand them.

There is a difference between code that is complex because it needs to be (ex: matrix mathematics) and code that is complex because you wanted it to be (ex: microservices and kafka and obscure functional languages for what could have been a Rails CRUD webapp).