Concepts (https://concepts.app/en/ https://concepts.app/en/) has been my go-to for several years. Several engineers I know use it for much of their draft work.

Concepts (https://concepts.app/en/ https://concepts.app/en/) has been my go-to for several years. Several engineers I know use it for much of their draft work. I don't do much beyond diagrams and wireframes, but I think it covers at least half your points, and the UI is pretty wonderful. Last I checked, you can markup PDFs in iCloud without importing / exporting, but YMMV.