Even with a properly managed team, moving 20+ years of edge cases and odd interactions for a turing complete game is going to be difficult. The fact that they need to come up with a usable ui on top of that only adds to the suffering. Its not unsurprising that what they currently have can only be considered working in the most generous and utilitarian sense.
Don't mistake me for covering for Worth: a top quality group led by management who knew what they were doing would be much farther in both correctness and UX.