The reason for this somewhat complex system is that 1. we want to present as much useful stuff as we can to modders while 2. artists should aim for the stars when making things. We want artists to aim for approval. I have talked to many that would feel like making high quality stuff would be less rewarding if their creations were deemed equals with simple geomerges and things people can whip out in an hour.
I think a solution to the problem of borderline approvable resources and rewarding the artists for quality work would be by adding Featured tag and possibly spotlight for such creations.
Like mentioned previously by
Chaosy, there are some gems in substandard section that are currently "hidden" from modders, which should instead be proudly presented by the website like all the rest since they are both creative and useful creations. Some scratch made models that are good quality but just too simple (ie. attachments) do deserve to be displayed since they can be useful for certain modders.
Also like
deepstrasz mentioned blizzard icons from other games being approved while simple geomerges aren't, I think some of the simple geomerges even though can be whipped out quickly can be really useful and creative as can be seen in most
Ujimasa Hojo's work, and I don't think it's a good idea to have them hidden in substandard since just by looking at the amount of downloads they have you can tell how useful they are as resources.
Besides simple geomerges are the most fitting resources when you're looking to create a blizz-like map and trying to follow the exact style of the original game (which to me seems like a goal of a lot of modders) in this case seeking the most useful resources this website has to offer for their projects would somehow be in the substandard section..
I would add Featured tag and spotlight for featured models to reward the artists quality work and give them something to aim for better than just approval, featuring their works would be a nice way to give exposure to talented artists and their creations. This would also separate the top notch quality work and simple geomerges or simply made scratch models while having both approved as useful resources.
Here's a mockup of the idea I have in mind: