Well, given that Maemo and Harmattan are actually more closed source than AOSP, not sure what weakness we're talking about.

It's solid to go towards one of the more open Android options than a dead and closed OS or UI that doesn't allow people to innovate. It's arguable that Android is a dead end but Fuchsia and the rest are not ready yet either for consumer products. Yet.

Maemo is dead. MeeGo is dead. Tizen is full of holes. Nemo is changing up tools and important bits at the moment. Harmattan is closed. Ubuntu Mobile was stillborn. AOSP is a dead end. Fuchsia is not ready. Jolla and Sailfish require licensing and planning for drivers that may limit hardware choices.

Opinions are aplenty. But adopt what makes sense. AOSP is looking the best out of all mentioned so far. But let's see what else comes about.