See, Larian said the game would be based on D&D 5e.
This phrase threw me off too and I wish they had never said it, because for a lot of us we interpret it as being as close to the original as possible but adding some things. This is not what was done here, and I know I would not have certain expectations of the game if this phrase had never been used.
Most movies/books/whatever that say "based on a true story" mean that the true story is shown as much as possible but blanks may be filled and some events slightly modified depending on the audience. A recipe "based on grandma's cooking" usually means that the old recipe has some tweaks to it but is mostly the same.
