The couple of devices I've broken down a release for and rebuilt just to clean out Trojans included in the firmware were devilishly difficult. And does it ever piss me off that there's nothing generic and updated to run on them.
As a user, however, it is severely locked down. Installing apps from 3rd party app store was okay-ish years ago. Nowadays, Android just frightens you as much as possible so that you don't install 3rd party apps. The battery thing that has already been mentioned is an issue as well. Nowadays you can't even use an alternate Camera app, you have to stick to whatever OEM gave you.
Thank you for the clarification! I haven't had the extra time to tinker with the latest devices since it's a bit outside my day to day. That's a bit more nuanced and it's good to hear from someone who develops on the platform regularly.