Memory is the smartest thing in this game. With 4 guys, having a character able to access a ton of abilities on the fly would kill character variety. Why bother making a buffer if everyone can buff themselves? Why bother setting up character synergies when everyone can just cast all the right stuff on themself? That's what happened in Original Sin. Without memory, character specialization would fall apart, and it's even more important for it to be a thing when there's 4 characters instead of 2.
That may have been the case on Explorer mode in D:OS, maybe even Classic mode, but if you wanted to play Tactician, your characters
had to be
specialized. Sure, maybe the Archer would have taken the Man-at-Arms skill "Helping Hand", but they had to waste a skill point in Man-at-Arms to get that skill.
That system is no longer present in D:OS 2, it seems. You're no longer limited by your proficiency in different spell schools, so I guess they chose Memory as the alternative limiting factor.
