It has been established MANY times in canon that the setting is very friendly to anachronism. I mean, hell, nine tenths of the main cast are swordfighters. They don't even use lightsabers, just regular old swords. Hell, two of them use STICKS. The setting is too diverse to say 'No, this should not be. Change it now.' Especially not with the table-flipping rage you're got going here.

It's canon fact that the Arrow is neither the first nor the most famous retrotech starfighter out there. Using your own logic, what would be so difficult about retrofitting the old design for modern aerospace combat? It's not like it hasn't been done before (US Air Force, anyone?), they just needed to figure out where to put all the necessary bits. The computers available would make it a relatively simple task to work out the designs. There's probably a guide on the UF equivalent of eHow on how to do it, considering how often it crops up.