User Defined "just" uses an ovpn that the user supplies. The wizard is not 100% full proof for sure, but if you're capable of managing a VPN server, then you're capable of debugging ovpn issues. Ultimately, if you don't supply a working ovpn, then it won't work, for sure....
If you don't understand the variability built into PiVPN, and the variance with the way people will set it up and use it, then nothing I can say will convince you otherwise. Either way, I'm not adding native support because it makes no sense. And I'm definitely not adding native support for your specific usage of PiVPN - that's way too limited an audience.
Also, I'm not even clear on the use case of PiVPN. If you're always connecting to the same end point just use systemd to achieve this. You'll still need a working ovpn for that though.