Privacy can definitely be easier to think about when the different parts of the service are considered together. A VPN may be used for ordinary browsing one moment and for a Wi-Fi connection the next, so having the relevant protection available without changing the whole setup makes sense. I also think simple controls are important on a phone because people usually want to get on with what they are doing rather than spend time managing the VPN itself. Looking at the privacy policy, connection options and everyday features together seems like a reasonable way to compare iOS VPNs.
K