There's no point having GSX trying to replicate a dedicated airport editor like ADE. Especially now that you can made a dedicated .BGL for GSX own use, that can be placed in the same folder as its related .INI file %APPDATA%\Virtuali\GSX
If you create such file with ADE and put it there, it will be seen only by GSX, so you could fix most of the problems caused by the lack of vehicle taxipaths and parking spots, which are quite common in 3rd party airports (default airports are usually better in this aspect), but the sim will continue to use the original .BGL, so if it was designed in a peculiar way for any reason known only to its developer, but it would otherwise confuse GSX that expects proper vehicle paths and parking placed in a realistic way, having a separate .BGL for GSX usage will improve GSX without having to modify the existing airport. And, you can use a dedicated editor like ADE, which has plenty of support and expertise to draw from.
The GSX integrated editor is best used to add things that are *not possible* with ADE and the .BGL format in general, like custom Stop positions, for example.