I think there are always going to be differences between the way PureOS is installed on an x86 computer (can boot from a USB device regardless of the state of the internal disk or disks) and the way PureOS is installed on the Librem 5 (the only boot options are internal eMMC drive or from host computer via USB using uuu, which means that if the internal eMMC drive contents are borked then uuu is the only boot option).
Ultimately both of them could provide the same disk installation options, with somewhat user-friendly GUI, but to make them offer the same options would be a fair amount of effort.
I guess it might help if @neva_blyad shed light on what use of LVM would be made on the Librem 5.
I think that in the past some customers have mused over the possibility of combining the internal eMMC drive and the uSD drive into a single logical drive.