I'm gonna have to disagree with this. While both make money on this deal, I'm not sure that Sideshow expected Prime 1's game to be so competitive. I wouldn't be surprised if down the line, Sideshow cuts Prime 1 from distribution in favor of their own statues. Also, I think the reason Prime 1 is fixated on 1/3 scale is because Sideshow currently holds a monopoly on the 1/4 license. Otherwise, I'd say Prime 1 would be making 1/4.
At this point, the price of a premium format is hovering around $430-500 and Prime 1's statue just about doubling it BUT from what we've seen so far, Prime 1's statues seem to be 100% the source material. In recent memory, what really turned me off to Sideshow's DC PFs is that new Batman Arkham Asylum statue. It looks absolutely abysmal. In contrast, Prime 1 is making a bigger Arkham Knight Batman that, in my opinion, is literally perfect, but double the price.
Keep in mind we haven't actually received any production pieces in hand from Prime 1 so it could be a total let down (and everyone will have their own opinion), but if I had to pick between Sideshow's DC Premium Formats and Prime 1's 1/3 Statues, I'd pay the extra for the [seemingly] infinity better accuracy and quality and the scale increase any day.
So I'd say yes, Prime 1 is in direct competition with Sideshow and I speculate it will be good for us collectors in both quality of product and competitive pricing.