I always keep the 3 libraries.
IBM (or your sysprogs) manage the contents of CSIQLOAD and CSIQAUTH when they install updates/upgrades.
(these need to be APF Authorised).
In the shops I have set up or worked at, I always get access to CSIQAUTU.
This gives us Endevor Admins access to Assemble the Customised Tables whenever we want.
(yes, I get access to LLA Refresh too).
Then we have User Exits that live in a 'site' dataset (stored in Endevor) that we concatenate into the CONLIB DD.
This site dataset is NOT APF Authorised.
If you put all 3 product datasets into one, then you could not concatenate a non-APF Authorised dataset with it.
System Rule:
Any Non Authorised Dataset in a concatenation makes ALL Datasets in that concatenation Non-Authorised.
Keep it Simple - Keep them separate.... IMO