Alright, those are actually quite easy to explain:
You need to use Glossy in linear space but albedo and specularity map in sRGB.
This is because 3ds Max's bitmap load dialog handles input color space, and it handles them based on file format. If your map is for example jpg, 3ds Max knows most of the jpg maps are sRGB, so it loads them as such. 3ds Max doesn't have artificial intelligence to know if you are loading diffuse map, specular map or glossiness, It's up to you to specify. Corona can't automatically modify gamma of the incoming map based on which slot it is plugged in, because not every pipeline is the same. Some softwares and studio pipelines save glosiness maps as linear, others as sRGB, there's no such thing as one standard. There are different conventions, some more reasonable, other less, but if Corona did modify color space internally in CoronaMTL, that would cause a lot more problems than benefits, because it would be against 3ds Max standards and expectations of pretty much all existing users.
I made a standart material with this maps and converted it into Corona.
If you use specular map in specular map slot in standart - Corona just dismiss it.
If you use specular map in specular level slot - Corona translate it as reflection.
But if you use it in sRGB mode you get reflectivity 4%.
Standard material is 3ds Max scanline renderer material, it is not Corona material. It has only very basic rudimentary support. And because it renders fake highlights without reflections, a feature which would be pointless and problematic to implement into physically based path tracer such as corona, only diffuse is supported, and specularity is "somewhat" translated to glossy reflection. But if you use standard materials with Corona, you use material of a different renderer. It's same as with V-Ray, which partially supports Mental Ray's Arch&Design material, but no one in their right mind would start shading their V-Ray scene with Mental Ray materials. The rudimentary support of the other renderer material is there only for rare cases so that unsupported material doesn't render completely black.