Their platforms are walled gardens, negating the alleged positive qualities.
Really? You really do not know what you are talking about. Apple has a lot of open source software. . . and contributes a lot of their software to the Open Source products, the latest is HealthKit. Some of the others are WebKit, which drives many of the browsers you probably use: CUPS, the printer driver used by UNIX, Linux, and many other open source printing systems. and even Apple's own underlying operating system is UNIX™, the ultimate open source software. Even Safari, Apple's browser's code is available for users to see. What you cannot do in iOS is freely load crap un-curated software that will compromise the security of the ecosystem. For that reason Android has 97% of the malware in the Mobile market and iOS has less than 1% and that is on the jailbroken iOS devices.
Yes, there are always "vulnerabilities" but exploiting those vulnerabilities is far harder with a walled garden approach. Allowing anything in, willy-nilly, and the platforms would not be secure or safe.