Jolla should select the hardware to have best possible control over the software for it. I currently use the Volla Quintus and when mobile data and WLAN is off over night, the system uses only 0.3 %/h of the battery. Since it’s a Mediatek CPU, power consumption increases massively with data connection. Android is much more power efficient, presumably because of the extended software possibilities for the hardware. There are example threads with Xperia devices in this forum discussing this relationship, e.g.
Jolla should select the internal hardware to get best possible control over it.