Also, there is no "requesting a specific upgrade". As you found, it's not very hard to achieve PC. You and a gazillion other people are PC status. As a PC you are eligible to choose from the PC section of Ultimate Choice locations. At non-UC locations, it's a guranteed upgrade to a Premium car. That's it. No upgrade for other classes.

Reserve a Compact car, get an Intermediate car.
Reserve a Fullsize car, get a Premium car.
Reserve a Premium car, get a Premium car.
Reserve an Intermediate SUV, get an Intermediate SUV.

While I know you had hoped the branch manager would pull out all the stops and upgrade you to an awesome ride, it doesn't really work this way. While a branch manager might do something for a very frequent renter, by and large, they don't have the time or inclination to be bothered by requests like this. He was politely trying to tell you that. I don't mean to sound harsh, but I wanted to be straight with you here as sometimes mismatched expectations can lead to other issues.