To be considered part of the RTS genre a game must have these 5 features.
- Resource Gathering
- Base Building
- Technological Development
- Indirect Control of Units
- Everything Occurs in Real Time
Resource Gathering
In RTS games worker units gather resources by mining them or constructing buildings in key locations to gather them. In DotA players get gold for killing enemies. This is nothing like gathering resources in RTS games. It is very similar to RPGs where players loot slain enemies for gold.
Base Building
There is no base building in DotA.
Technological Development
There isn't any real technological development in DotA. Players can level up their characters and get new items and abilities, but this is exactly what is seen in RPG games.
Indirect Control of Units
Typically a player only controls a single unit in DotA and it is controlled more like it is controlled in RPG games such as Diablo.
Everything Occurs in Real-Time
This is the only feature out of the five that DotA actually has, but so do millions of other games and other genres such as First Person Shooters. To be considered an RTS a game has to have all 5 features.