I have the same issue, ZTE Tempo X with an SD card as a save location, and I'm not using the SD card to store apps. However, I have a little over 2 gigs of apps, which I don't think is that much compared to most people (I've deleted most of the apps the phone came with, too, at least the ones I *can* delete). That, plus the mysterious 5 gigs of "System memory" that I can't seem to access or delete, and my phone is just shy of it's maximum 8 gigs of storage. I now cannot update any of my apps without deleting a bunch of other apps.
I would love to delete a lot of apps on my phone that I don't use, such as "Amazon Shopping", "Browser", "Facebook", "Messenger", "Gadget Guardian", ******* "News Republic", etc, but the phone won't let me.
I'd love to clear out some of the "System memory" that is taking up nearly 3/4 of my phone's space, but I'm not finding any info on what that is, or how to delete any of it.
Other than going thru all my apps and deleting their data, any ideas on how to manage about 3 gigs worth of apps on this phone?