To some extent Android has won on mobile the same way Windows won on the desktop.

It's true but kind of irrelevant because this is not what Apple was ever after (otherwise they would have pursued a very different strategy, with 3rd party licensing, etc.).

Does it really matter if Apple's market share is declining as long as they keep capturing >80% of all profits from said market?

As long as they keep their target demography on board (both on the consumer and developper side) they'll do just fine.