My experiences with lugers and P38 are minimal, but I am not aware that a luger with proper magazine and properly tension springs is unreliable. Perhaps they will not tolerate a lot of dirt, but they normally were carried by officers in a very protective holster. As already mentioned the luger was not as easy to manufacture as was the P38.
today neither is an attractive first choice for self defense since we have better guns. Most lugers are 75 years or older in age for sure are for the target range and not for combat after so many years.
The Lugers that have Waffenamtabnahme stamps were issued to enlisted men. Commissioned officers had to buy their own sidearm and uniform, as well.
The original DWM manual " Die Selbstlade-Pistole "Parabellum" " is giving the ammo specs of the 9mm Parabellum load as 8.0 gr bullet, a velocity of 310 m/s and 39.18 mkg. It is important to have ammo in the same power range for proper functioning.
I even shoot one of my P.08s with 125 gr truncated lead bullets with excellent accuracy and reliability.