hey_it's_that_dog
benevolent sexism
You can tell the developers exactly why you're dissatisfied with their product so it's not like they'll suddenly say "oh, low sales, means nobody likes this franchise". That's only the case if you don't actively communicate with them. But according to many who opposed us in the original threads, sending a tweet to a developer expressing your views is a ridiculous thing to do.
People should absolutely communicate to the developers however they can that they are angry about the deception (whether it is willful or accidental). However, the devs have no way of correlating non-purchases with user complaints over twitter. I mean, you can't correlate non-purchases with any variable, but the point is that direct complaints don't serve to clarify the motivation for non-purchases.
They will know their sales figures (and how they compare to the other Souls games) and they will know that some people were unhappy about the downgrade, but they aren't going to be able to synthesize that information into something useful. Even if the game sells worse than its predecessors AND they have lots of complaints on Twitter, they cannot logically conclude that the complaints are a major reason for the sales decline. There are too many other variables.
In summary, do communicate your dissatisfaction, but carefully consider whether a non-purchase is sending the message you intend, or whether you're just screwing yourself out of an excellent game (and failing to vote for more excellent games in the future).