Halo Wars sold 16.7% of Halo 3’s first week sales according to Wikipedia.

It was commercially successful but not in a mainstream mass audience kind of way.

Yes, it proved that RTS can be done on a controller (arguably, StarCraft 64 kind of sort of proved that, too), but if you’ve ever played StarCraft 2 I think you’d agree that particular style of RTS is really not possible without a keyboard and mouse. The game is almost entirely revolving around maximizing your actions per minute.

I also think the RTS genre is very much less popular today and then it was at that time.