I thought Valve didn't have bad developers
OH WAIT
And DotA is NOT a mod and was NEVER the first AOS type map either. It's like saying Badwater was the first Payload map and then making thousand slightly different versions of Badwater.
It's just a map for WC3. Thing is, maps are way more customizable than, say, in Source. All of it has been made in the editor, there was no external modding involved. Heck, adding a custom texture is already more "modding" than making a WC3 map.