So how many seats are needed to hire somebody who creates a custom shiny + R app that does exactly what you want? How big is the average company that makes use of tableau etc.? Let's do the math ...

It’s 2019. Are we seriously still trying to argue that homegrown solutions are overall more cost effective than SaaS? Are we still of the opinion that developing tooling outside of your company’s core competencies is somehow adding value?

Absolutely. There are tons of people I encounter every single day that seem to think it is cheaper to build everything inhouse. I think it comes from a complete misunderstanding of how business delivers value coupled with RMS-like distrust of anything they cannot completely crack the lid open and mess around with. Mostly the former, some of the later.

Well it's probably a question of perspective and problem domain. Also my main concern is precision and correctness. Quite often you can choose between (1) customized tools that achieve almost what you want them to do, but often the people who implemented or customized them didn't fully understand the problem and did things wrong without anyone noticing for a long time, or (2) custom tools that do exactly what you want, that were tested by somebody who cares.