You seem to not be thinking about the team of people who tracked planes from other forms of communication and the relayed it to those who needed it. The display on the map is not meant to simulate radar, but rather a collections of sightings.
You may or may not like it , but don't try use a simplistic "radar" didn't do this, when that is not what the system is supposed to be doing.
HiTech
True, aircraft tracking and communication relays existed. It was able to tell groups of aircraft the approximate location, altitude and direction of travel of another group of aircraft. However it was still a blunt instrument and was designed to guide fighters to contact with the enemy.
In the iteration we currently have in AH it is possible to manage your individual fights because the radar is so accurate. I can tell when an enemy plane changes direction in real time so while I fight one aircraft I can manage 2, 3 or 4 others just by referring to the map. If I ever lose sight of the enemy in a fight I can just refer to the map and it will tell me not only where they are but also where their nose it pointing. Classic 'bounces' or 'lose sight lose the fight' simply no longer exists.
Diving into the clouds was a legitimate form of evasion. Not in here, just track using the map or via the plane highlight function available with the tab button.
Using terrain to mask your movements is not possible. If I lose sight of a target I am chasing because they manage to go around a hill and break my visual contact I can just monitor the map to see if they reverse on me or make any other changes until I can clear the crest and regain visual contact.
This is the level of detail that the radar gives at the moment. I think it detracts from the game rather than adds to it