I mean, in principle I don't disagree. A quantitative kpi that shows before and after is usually measured differently for each product you're building docs for.

For example, if you have a developer tool, the number of devs you can successfully onboard after you have solid documentation up and running is an effective strategy for getting unimaginative middle managers to understand the value.

Generally the people I work with have already come to the right conclusion because they have tried everything else and not gained the traction they believe their product deserves.