Can't help with documents on this I'm afraid.
Your contention is sensible from a fresh pair of eyes but at the time the slow development of centimetric radar for the Germans bred an extreme conservatism in territorial air defence, which centred around FlaK and only begrudgingly with night fighters as it was...the first nightfighter groups were established as independent ventures, many rather successful projects began like this because most Nazis running the nation were basically unqualified twats. Let me put it this way, the nickname in the military for burgemeisters and governers was "golden pheasant" but they basically ran the show.
This is the sort of thing which is meant by historians such as Dr Martin Kitchen when he attributes most strategic blunders to an extreme organisational disarray inherent to the Nazi Party which, on one hand allowed Hitler to maintain an absolute dictatorship but on the other created a large, unwieldy, mostly useless political organ that stifled anything opposed to it.
The general support of the Nazi infrastructure simply wouldn't back placing defence of the cities on something as experimental as radar, Kammhuber received support mostly as an afterthought at first and later purely by necessity when faced with thousand-bomber raids. At the start of the war the development centres in Germany had actually proclaimed the development of small wavelength radar was technically impossible according to Walter Boyne, and were utterly shocked when a Lancaster wreck was examined to find centimetric AI radar fitted.
In 1940 there was still little support for nightfighter operations and the defence of the Reich was trusted entirely to the FlaK regiments, which was considered an elite organisation capable of stopping aerial intrusions using a sheer wall of fire. To their credit it's pretty much about right, the biggest danger to daylight raiders at this stage wasn't interception but FlaK, although interceptors could maintain pressure outside main areas of coverage and chase the intruders halfway home.
So I think it was largely political, partly conservative and spoke about the needs of the day. Perhaps shortsighted, but nevertheless detecting and bringing down bombers in daylight until 1943 wasn't at all an issue.
In terms of an early warning system, the German answer was (aerial) defence in depth. The only vulnerable region was ports like Kiel and they were fortresses, the infrastructure was immune to aerial bombardment until the Tallboy bombs, the FlaK concentration was downright scary and they were major fields within the interception zones of JG2 and 26 and their höhestaffeln. In 1942 only Mosquitos had a decent survivability over German ports, I mean sure they got bombed but only moorings were vulnerable to it and the attrition to bombers was pretty bad.
So mainly the issue was bomber detection and tracking at night, which otherwise avoided much FlaK and most interceptor defences. And even that took some time for technology and conservatism to catch up with necessity. It's also telling that the Kammhuber system even as it evolved never guided FlaK but was used to direct searchlights, so the elite FlaK crews or interceptor pilots could see.
And I think this also speaks about something political. To centre an expensive and complicated aerial defence system upon radar direction would be to admit that intrusion/invasion was a foregone conclusion. It's not something I think any of the major Nazi figures were ever prepared to do.