So then why is it when the Memory Hoarder is killed, it's said there are souls twisting around it?
it's own soul maybe fractured by the memory of hundred
even maybe it was created the same way as some other powerful animate did
I get what you're saying.
Just looking through walkthroughs and other hints the past couple of days though, it does seem the souls in the Assembly of Echoes that rise up during the fight and the souls in the Memory Hoarder are part of the Collection of prisoners. One note talks how a guy lost part of himself and felt it go into the maw of some creature down in the pit.
I'd have to review it all again but yeah, it also does seem the Memory Collector is a creation of the Oracle in Wael (the one guy mentions it when you ask him what is that thing)