I like use case diagrams as well. Thing is these should be short lived and used to make specific illustration in specific time. Not some holy grail of documentation that people should take as some god given truth for whole life of the system.
"The following essays by Jack W. Reeves offer three perspectives on a single theme, namely that programming is fundamentally a design activity and that the only final and true representation of "the design" is the source code itself. This simple assertion gives rise to a rich discussion—one which Reeves explores fully in these three essays."
https://www.developerdotstar.com/mag/articles/reeves_design_...