I really like the UPZ boots, well, “shells” a lot. Agree, the original liner is really not the greatest, but that’s the case with almost all liners out there. Especially if you have “special” feet! I learned several years back, that no matter what original shell/liner I used, they all didn’t work great with my feet/ankles. Even the Thermoflex liner was not helping all to much (They packed out on me after riding a couple of hours). Ever since I use foam injected liners (Strolz), I can pretty much use any boot shell there is.
I think, it’s more the liner/insole combination (with some good boot fitting skills, if needed) what makes all shells out there work… at that point it’s back to preference again, what shell design/mechanism delivers what power transformation/flex pattern…