Correct me if I'm wrong 1: so sce's are overlays and to be independent from each other they contain their own dependencies from ground up. Which means that we end up with multiple copies of tar for example, each sitting in every sce which ultimately takes up more space and possibly ram if those are actually loaded. A logical solution would be merging multiple sce's into 1 custom sce.
Correct me if I'm wrong 2: there is no official tool for merging sce's. If I was to do this manually, I'd have to redo this after an update