In my experience, companies mostly use Confluence, Atlassian's Wiki, for this sort of thing. It has a bunch of plugins for diagrams, from Visio-like stuff, to more Photoshop-style.
I completely agree! I'd love if you check out our competitor; it's a hosted version of Wiki.js that's a lot easier to use than Confluence. It also supports direct diagramming in SVG (Draw.io built-in). http://miki.mimix.io
The problem is that it's simply awful to use.