You should be able to delete the ifscoped routes if you give -ifp INTERFACE as an argument to the route delete command.
And I found this explanation about Apple’s default routing selection for you:
If you look at the routing table on an iOS device using a tool such as System Status, you will see that when multiple networks are available at the same time (such as WiFi and cellular), iOS will usually mark the lower priority interfaces with the RTF_IFSCOPE flag (“I”) and the interface without this flag will be the dominant interface, where OpenVPN or other network apps like Safari will open connections on this interface by default. Normally, iOS considers WiFi to be a higher priority than cellular data, so if both are available, iOS usually sets the RTF_IFSCOPE flag on the cellular data interface to favor WiFi.
From OpenVPN ignores connected WiFi and uses cellular data - OpenVPN Support Forum