8K altitude limit? So, you'd effectively gimp all fighters that have advantages when fighting at alt and make this arena a festival of low-speed TnB fighting in the weeds? Ok, whatever, but you'd make half the planeset ineffective because they couldn't compete with the low-alt turners. To make this a proper fighter arena you'd have to make those cliffs 30k high and add a few new areas with medium-alt and high-alt bases or air spawns for the 152s, Spit XIVs, P-51Ds, F4Us and so on. People rarely fight at 20k in the MA because no one wants to waste the time climbing that high. Take away the climb time and you can set up some interesting fights that you never see in the MA (such as a Ta-152 actually being effective at something!).
In the end the DA is good enough... you're just adding big walls to segregate the fights.