Who in their right mind would do such a thing. Even if the competitors really are stupid (who knows?), it doesn't give you any advantage to assume that.
Once it finds such a thing, subconsciously the mind registers the competitor as weaker than they actually are, to redeem your mind from the uncomfortable prick of a all-powerful competitor. It doesn't happen for everyone though. It takes a bit of rationality to overcome such conclusions.
I personally know people who'd read and stress negative reviews of their competitors' products, and eventually conclude that their competitors are not really thoughtful in their decision making.
TL;DR - Yes.
So can we assume people who assume other people are stupid, are stupid? Or is there some benefit from doing things that way that might not be apparent at first sight?
One possibility that comes to mind is the substitution of parallelism for serial processing, or put another way, letting the world be its own model. Instead of one startup spending a lot of time thinking and researching (and maybe missing the market window if there was one), let ten startups just assume and go for it. Maybe nine will be wrong and fail and one will be right and succeed.
But that'd be something like evolution or anthropic computing. In order to find a solution to a hard problem, write down something. If it is not a solution, kill yourself. Conditioned on looking at anything at all, you look at the correct solution.
Or we could use the distinct advantage of humans and think about it properly.