Lets Sell The Idea -

I played Age of Empires II in High School, back when it came out. I played competitively online, a relatively new thing. There was also fan websites where people shared what they produced on the campaign editor. I liked Mrfixitonline.com. (I believe that is what it was.)

As a middle class family, AOEII was the only game I was going to have for awhile. The campaign editor greatly expanded my usage of the game, where on the weekend, I could try out and enjoy some of the better fan made content. There was a fan made multiplayer mode where they put the game on slow, used regicide, and a rivers map, and focused on a longer game and diplomacy. That was fun. I haven't had a lot to do with Age of Empires II in a long time, however, someone is still pumping out expansions for the game, and people are buying them. It may be due to having created this online community of people sharing fan made content.

Warcraft III also had a campaign editor. A lot of interesting fan made multiplayer custom mods ended up created. Something like DOTA, which also spawned League of Legends, that started from casual players playing around with custom multiplayer mods.

Given someone created an RTS game, and didn't launch it with a campaign editor.......it is less than, and the developers were gimping themselves.