Game is amazing there is no doubt about that, but I agree with you OP.
Just to add few more: 1) Fish folk you meet in the Underdark where if you killed the redcap could tell them to start worshiping you and/or build you an army. They are nowhere to be found after that in any of Act 2/3. 2) Many notes and letters which should lead to quests in Lower City are not working and are just for reading. Apparently they were cut from the game.
If you wish you can add these to your list.
As for the rest I fully agree with you. In some of the cases datamining is not even needed to clearly see that content has been cut out.
