It was more that they would rather send Monarch an RPC than be connected to. Not everyone wants e.g. an HTTP server in their process. For example maybe they are security sensitive, or have a limited memory envelope, or other reasons.
Amusingly in the pre-web 1990's, at Telstra (Australia telco) we also developed & implemented a custom performance monitoring library that was integrated into in-house applications.
The phrase 'you aren't Google' is true for 99.9% of us. We all get to fix the problems in front of us, was my point. And at that scale you've got unique problems, but also an architecture, imperative, and most importantly an ethos that lets you solve them in this fashion.
I was more reflecting on the (actually pretty fine) tools available to SREs caring for off-the-shelf OS's and products, and a little on the whole 'we keep coming full circle' thing.
Anyway, I very much appreciate the insights.