I think the hardware is a limiting factor, but part of what makes these devices unique (as other commenters have pointed out) is that they can run with minimal proprietary blobs. I don't believe either phone is at "no blobs" yet, since even Purism had to have blobs for the Baseband and Wifi (I think, or maybe it was just Wifi?). Nevertheless, Ubuntu Touch does work on Android devices today, and I think even PostmarketOS has some adoption on OnePlus 6/6T.
Overall though, I'd say that power isn't really the big thing. I think existing software has shown that you really don't need a lot of compute to be able to run apps smoothly on these phones (Morph browser, many GTK apps on the Librem 5). Battery life remains a concern with these devices, but that seems to improve bit by bit over time (at least, the Pinephone does. Not sure what is up with my Librem).
I think getting a partnership would be doubly tricky though, because a lot of the market just doesn't want these phones to begin with, and struggling companies are unlikely to attempt to explore mobile Linux unless they know it'll turn their ship around. Maybe if they get banned from using Android somehow (much like Huawei was), but even then I can't say I'm sure that Linux is appealing for companies in that scenario.