Just because you disagree with them doesn’t mean you’re not wrong for saying there is zero disadvantage. The disadvantage is not giving customers what they want.
This isn't something that can be A/B tested when there's only one (thinner) offering. People "need" to upgrade their devices and will ultimately buy and put up with the newer model even it means trading a decent keyboard, potentially better battery life, or a headphone jack.
By the same logic, if a crappy movie (by reviews) nevertheless earns a good profit on the first weekends due to an intense marketing campaign and flashy, misleading trailers, that would magically make it a good movie, because obviously "customers wanted that".
No it means consumers think they want thinner phones, not that they actually prefer using them in practice. That's what marketing means.
And of course, the reason they think thinner is better is also marketing. Keep repeating something and people will internalise it without criticism.
There would have to be two otherwise identical devices, one thick; more robust; larger battery.
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.
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.