One man's shit is one man's treasure.
ConnMan fully supports VPN configuration. The reason for choosing ConnMan over the legacy networking system is that while it worked for you, the large majority (99%) of our users do not wish to configure networking via a command line. ConnMan provides us with a stable DBus interface so we can make configuring connections simple and manageable from Kodi. It also has a very low footprint.
It is easy for you to copy over /etc/network/ files to remedy the situation, and that's what we expect from power users. We need to support the most common use case scenarios and make these as easy as possible for users to employ. ConnMan lets us do that.
With that said, I don't anticipate a reason why we won't have GUI based VPN configuration eventually
Here. What would you consider as more established? NetworkManager is a lot more resource intensive and wouldn't work any magic: we'd still need to develop our addon to support VPN via the GUI, and additionally, have to rewrite all of the networking code.
If you can provide a better description of the issue then we can have a look.
You are likely being caught out by WISPR. To determine true network connectivity (and in the future, to allow login to WiFi networks that ask for a username and password), ConnMan will configure a route and try to connect to osmc.tv. If it receives HTTP-X-OSMC then it knows that it is really connected to the Internet, and not a web page asking for credentials.
I see you are using a legacy /etc/init.d/ script. The solution is to write a proper systemd unit (I am sure one already exists for OpenVPN) and add
ConnMan assumes that as it is the network manager it is permitted to configure routes accordingly. Other network managers will do the same