Most of the “Is open source software safe?” section of this post seems to advocate for what’s conventionally called Security Through Obscurity, which is widely considered very ineffective at preventing exploitation and at best a minor hurdle.
There are a lot of differences between Android and iOS in terms of security, attack surface, and exploitation, but attributing that to open vs closed-source completely misunderstands the entire subject. For just two of the countless reasons: Many of the worst vulnerabilities that affect Android devices are in closed-source proprietary Qualcomm firmware. A platform being open in the sense of allowing users to install any application they want to (like Windows and Android to a limited extent) or closed off to prevent installation of unapproved software (iOS, PlayStation, Toyota cars, TiVo, etc.) is completely separate from whether that platform is open-source or not. GPLv3 has license terms that try to tie the two concepts but I chose examples that don’t use it at all. Also, iOS has public kernel source code.
There’s a good reason for that one: the first animal crossing game was originally made for Nintendo 64, though that version was only released in Japan. GameCube got a port of it and that port (plus some extra features) is what released in English.