Apparently, asking for individual edition answers in the dungeons-and-dragons tag is too broad; is the proper procedure for such cross-edition questions to ask one question per edition I'm interested in, or is there something else I should be doing with this?
Tagging wise you're asking the question correctly, using either dungeons-and-dragons as a spanning tag if you're talking about comparison across all/a lot of editions, and 2-3 specific ones if you're doing a more limited comparison. The tagging isn't what's wrong with that question.
"I want comparison of 5 editions" should not garner 5 answers each of which just talk about one edition. No answer is then correct and helpful unto itself. If you want a comparison of X over Y, you need to wait for someone that understands X over Y to answer. That's the price of wanting a big expansive answer (well, and the price of "too broad" which it can bump up against).
Also consider what problem you're trying to solve. "Curiosity" isn't much of a real problem and often people will vote that way. Remember on a SE you are asking people to do work to help you. Just asking them to "write a dissertation because it amuses me" is less well received, and that's just life.