I give this an upvote grudgingly because it is a useful article, but quite depressing. Why can’t freedom-respecting computers also be secure?
Linux (as it is shipped with most distributions) is not secure either, or not as secure as it could be unless manually configured and hardened with extra modules. Convenience, I guess. What I take from the article is a similar situation, I think. Android gives you a restricted customized, modified Linux and all the environment around it. As a user your only freedom is to install apps, use apps, uninstall apps. It’s restricted by default. On the hardware side and maybe firmware as well: nothing we can do.