Hi Christian,
What you write makes perfect sense - what you should note is that OH2 just started in the direction of “UI-driven setup” and is by far not yet at the goal; especially as there aren’t many people contributing to these parts and it is a huge effort to get those things working.
See my post here. What you describe would be for users of the second category (all UI/database). I am not sure if it is wise to couple the items directly to the channels (and not show items at all to the user anymore). I can consider something like this as an “easy mode” to enable, but this would be too constrained for power users. Take e.g. KNX (this was the very first binding that existed for openHAB): As a thing, you could have a 12-channel actuator in your cabinet, switching lights in 5 different rooms. Using the name of this actuator for your items simply does not make sense and it would couple you to the specific hardware; you couldn’t e.g. easily replace by a Philips Hue bulb the next day without having to adapt all your rules & sitemaps. This is where the separation of the functional item layer and the physical devices is very powerful and handy.
Nonetheless: Yes, an interface builder would be nice and there are discussions for the server side for enabling such UIs. Are you a developer and would be willing to help working on realising your ideas?
Regards,
Kai