As a fun anecdote, in 2014 when the "secure" Storage Access Framework was new, I found a trivial directory traversal vuln that allowed writing to any app's private directory by just passing a "../../" file name to the system [0, 1]. It was so trivial I noticed it while just browsing AOSP source to understand SAF better...
Android also used to grant world execute bits to app folders for the longest time, allowing malicious apps to create hard links to other apps' files by name, which could then be handed back to that app for a confused-deputy attack to gain access to the file contents.
All that to say - I'm glad Android has been working on security, but it was built upon such a loose foundation that tons of apps used and abused that it's going to drive developers out of the ecosystem as they have to keep adapting to a continuous stream of major breaking changes as things are locked down.
[0] Bug 18512473 fixed in https://android.googlesource.com/platform/frameworks/base/+/...
[1] Proof of concept video: https://www.dropbox.com/s/8dpd8visrttqbfo/poc.mp4?dl=0