Your inquiry comes just as I am finishing up a presentation on interval training for our upcoming San Diego clinic next week. See section 4.1 and 4.2 of https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8294064/ for the benefits of those CFo21 (Zone 5, HIIT) intervals. That meta study says it better than I can.
You’re right on on #1, but those short CFo intervals don’t really promote your #2 and #3. The RCI and CCI series do a better job of promoting your #2 and #3.