> It prioritizes concision and an abstracted ideal of "readability"[1] at the expense of mental model and ease of use.

That statement applies to all format strings, which are by necessity a small internal DSL. For the = syntax, the input is copied directly to the output with the value of the variable appended. Within the realm of language features, sure it's one more chocolate wafer of syntax. Within the realm of format strings, it's certainly more straightforward than the type conversion and padding syntax.

> That particular "=" syntax is really mostly just useful for dumping runtime state at debug time.

In scientific / ML development that's like 80% of the work.