I think it will all depend on your specific lighting needs and how subtle the effect has to be. If you are trying to replicate lighting found in ray tracing and the subtleties of low light conditions and do this dynamically bouncing from interior to exterior or low light to sun light you are going to be in a difficult situation.
Depending on your scene complexity adding physical lights may make the scene overly bloated and non performant, where as baking two sets of textures (exterior and interior) may not be practical…then you are left with very few choices.
Equirectangular vs CubeMap…I think thats a subjective call depending on your scene needs and wether the poles created in a equirectangular map are really causing an issue or not. From the sounds of it..they arent…its just that the HDR you are using is casting too much light for your interior scene.
The good news is the Verge3D_Environment_Shader material is accessible through the material puzzles. This allows you to use Mix Shaders that allow you to add filters to an HDR or mix between 2 or more environmental textures to get something you like or two change from day to night, interior to exterior. Just don’t animate them bad stuff can happen but have had no problem swapping settings unless this is for mobile deployment…then it may be a big tough.
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