I bet there’s different schools of “sustainability” to this claim. On the one hand there’s the people claiming that if you want to be truly sustainable, you need to aim for minimalism. Pulling that to extremes you might argue that a full smartphone wastes more resources than say a candybar shaped dumb-phone (not to mention the increased power consumption), so perhaps we should all live a bit more modestly. If people are willing to drastically restructure their diets to give up say animal products, giving up facebook and whatsapp on-the-go sounds to me like a relatively insignificant sacrifice.
On the other side (for those that question my objectivity,I’m not this is the side I’m on as well) there are a lot of people who feel sustainability does not have to come at the cost of functionality. This brings us to a different “trade-off” space where we aim for ethical production and longevity on the one hand, and finding a feature and performance point sufficient for the masses on the other hand. When navigating this design space we need to cleverly think about the “high-end” features that we discuss. Adding a high end SoC with fat cores and an even fatter GPU might make the phone more attractive for some gamers, but judging by the size of the market for OnePlus, Wileyfox and the likes this is not a deal-breaker for the majority of the people while burning through batteries and energy quicker. A high-end feature like 5G over a broad range of bands however makes the phone more feature-proof as there will inevitably be a point where provides choose to drop backward-compatibility with older standards. A low-end SoC from a cheaper manufacturer is less likely to obtain (security- or full Android) updates two years from launch when compared to the established mid-range SoCs, meaning again that the lifespan of the phone is increased by going more high-end. Not to mention it’s hard to judge what app requirements will be in three years, other than that we know they’ll be higher than they are now.
All things considered, as much as I sympathise with your call for realistic specs rather than aiming for the shiniest of shiny, we might still need to have a serious discussion about how high we really need to set the bar!