Nowadays the situation has improved with FBX but a couple of years ago it was a serious issue
At the time , Gekido ,the bad guy , supported his clients while the nice Unity army let them down , at least in this occasion

A part from that it is really a shame that GameCore has been abandoned

As you said , GameCore editor is at the state of art but in my opinion also the programming side is excellent
GameCore supplies 700 + function and they are all meat
You dont have to reinvent the wheel but at the same time you have about the same flexibiliy as using opengl or direct x
Obviously people can not expect to learn a powerful engine in a couple of days
Angel scripts is not an unknown scripting language
On GameDev there is even a dedicated forum
Just compare the clean GameCore code with the ugly, at least for me, components based Unity programming style