Multiple IDs single user (for security) but APPs are for single ID & Family Sharing as workaround is disappointing?

IMHO, there are reasons such as

1. security for multiple IDs (some websites don’t accept Hide My Email).
2. consolidate previous devices (with old IDs created to carry meanings which became outdated due to changing circumstances such as geographical relocation) to single device with new ID.

Unless paid APPs recognise different IDs and please correct me if wrong, merging data to new ID is imperfect, I wish Apple can feature multiple IDs for single user due to following limitations:

1. paid APPs are not yet smart enough for multiple IDs with single user; subscriptions aren’t recognised on device with different ID.
2. Family Sharing is my workaround but it doesn’t always work; and I have to bear with less features of free APP even though it’s paid or pay again on device with different ID