I'm pretty sure marketers and designers really do know that. How light a device feels in the hand is pretty much the very first thing someone notices when picking up a new device, and sets the stage for the rest of their expectations.

We also know that in most cases (of course not every case) first impressions are a much bigger influence on the final decision to purchase than later analysis and consideration, regardless of what people think about their own decision making process. Pretty much every company that has ever sold anything cares about this stuff, and many of them have plenty of resources, so this has been studies to death for decades. A lot of super smart people have spent a huge amount of time devising very clever ways to test this stuff.

> We also know that [...] first impressions are a much bigger influence on the final decision to purchase than later analysis and consideration

But this is the whole point of the GP's criticism: The whole design of the device is driven by optimizing purchase, not actually by making it usable, useful or durable.

Of course we can know that. Basically all manufacturers save apple have a very long tail of non-flagship phones which nobody really pays much attention to, but which absolutely can answer questions like that. They have dozens of models, mostly basically identical save for minor changes.