I can understand that it felt crowded to you, but what you reported actually matches up pretty well with what the crowd calendars predicted.
You stated that overall, "Monday, Tuesday, Wednesday and Thursday were the least crowded days at all parks (Disney included)." For the first week of February, Undercover Tourist had Sunday, Friday, and Saturday as the most crowded days of that week for all theme parks (all three were listed as yellow / moderate, while Monday-Thursday were listed as green / low). Orlando Informer has Sunday and Saturday listed as moderate, with Monday-Friday at low.
So, both guides actually match what you experienced.
As for Saturday being as busy as it was... again, it's all relative. They stated that Saturday would be the busiest day of that week, and it was. And while it sounds like you feel that the crowds were well above Moderate ("complete chaos"), you also said that the wait for Gringotts was over an hour. During really busy times, Gringotts can approach two hours or more. Did they block the entrance to Diagon Alley? In general, the really crowded days occur when the entrance is blocked (i.e. you have to wait or get a return ticket in order to enter Diagon Alley), and on those busy days the it can block well before noon and stay that way through most of the day (I've seen reports where people have gotten there at 10:00 am and received return times for 7:00 pm). If you did have to get a return time for Diagon Alley, then the crowd calendars were probably wrong, and it really was busy. If you didn't have to get a return time, then what you saw was unfortunately "average" for Diagon Alley.