Nice summary. Tooltips are great for self-guided discovery when there's a cursor; what about touch interfaces?
For example, on Android, long pressing an icon in the top bar of an app will show its label.
Tap on a bubble and it expands into a larger one or navigates to a separate help page.
It is an effective way also to learn an app - by doing, not reading.
If you need tooltip or guides like those, your UI has other serious issues.