You weren't forced to upgrade. It was offered and you accepted. You would have still got security upgrades on V9 (from Google) for some time. Many people don't get an upgrade, let along a choice of refusing it.
Re UX, you don't have to use gestures. You can opt into the "traditional" three-button system.
the three buttons no longer work as before - e.g. long press no longer does split-screen. Furthermore, the UX before was cards one on top of each other, the open app is the topmost. The current "logic" is with cards sideways. Which is ugly, non-intuitive and copied from iOS. If you move left to take another card, suddenly your previous card does not remain on the right side. How is this intuitive? Even from business perspective this does not make sense, because once I got used to the new non-intuitive and less efficient UI, the switching costs to iOS for me will be lower.
When you say non-intuitive, you're not talking about intuition. Holding a button for split screen not intuitive, it's just something you've learnt. Rows vs piles of cards are essentially the same thing, each with slight benefits.
Reforging muscle memory is an inconvenience, but if Google thinks it has a better UX (copied or not) for non-indoctrinated users, maybe it's worth learning another way.
And the similar-UX business case works both directions.
We wouldn't have the things you're hanging onto without that sort of development.