That might be true, but at the same time you shouldn't run random scripts off the internet as root, even though there are plenty of EoP or RCE exploits. The same applies to letting random apps get privileged permissions, even if sophisticated attackers can bypass those permissions with 0days.
>System partitions cannot be edited due to SELinux and also thesedays the partition ext4 is created with certain blocks - cant be changed.
That's irrelevant on Android because system apps can be updated without touching the /system partition, if the .apk is signed with the same key. The system will store the updated .apk file in /data/app, but otherwise grant it privileged permissions that only system apps can get. That's how google play services can update itself and still keep its privileged status, even though the phone OS hasn't been updated in years.