This is one of the majors problems with completely locked-down platforms. Assurances that the owner of the platform respects your privacy and prevents others from violating it are really just a pinky promise.
The key question is whether Apple will play a curator role in trying to reign in the ecosystem. They have in the past (eg Uber was doing shady shit and there was a game of chicken to get them to stop). Of course Alipay and WeChat may be harder especially how Apple China is such a huge market for Apple and critical to their success now. It’ll be interesting to see how Apple adjusts to this over the next few years.
Open platforms also have this problem and also operate on pinky promises (perhaps even worse) so I’m not sure the point you’re trying to make unless it’s that “well if this problem isn’t solved I’d rather have an open platform”. The problem with that argument is that there are many issues and this is only one failure case which may be addressed in the future whereas open platforms have this one and many more that are unadressed.
For what it's worth spyware/malware consistently seems to target Android more than iOS [1]. To be fair Android has more units, but that's just one axis - iOS users should be more valuable to exploit because they're usually in a different socioeconomic bracket. Another data point is that Android developers get paid anywhere from $2k to $20k to add malware to their Google Play store app [2] - I can't find any articles similar for iOS so would be interesting to compare the marketplaces if anyone knows it for iOS.
[1] https://nordvpn.com/blog/ios-vs-android-security/
[2] https://www.bleepingcomputer.com/news/security/cybercriminal...