I'd like a confirmation from someone of Larian before I delete that folder.
I get that completely but I can say it definitely works for me - you only need the "DefEd" folder which is only 20GB. If something goes wrong you can always restore the "Data" folder back.
30GB saved on a 120GB SSD is a lot especially as I'm not going to play the old version again - it means I can have Pillars of Eternity 2 installed at the same time.
I would have been more convenient if it was released as separate game like DOS EE but there we are.