While I've absolutely had this experience with some of my ARM boards (notably, most of my ODroids are stuck on some variant of the 4.14 kernel with vendor patch

While I've absolutely had this experience with some of my ARM boards (notably, most of my ODroids are stuck on some variant of the 4.14 kernel with vendor patch sets), the essential parts of the espressobin are in mainline, device tree and all. The larger problem of developer/security team time and effort is still there, though. Arch Linux ARM and Armbian are active and well-maintained, but I do find myself running into problems that indicate that the community of active users for this type of hardware is vastly smaller than a traditional architectures.