The week of Thanksgiving (this year on 11/28), usually a lot of school districts surrounding DL have that week off and so the days leading up the Thanksgiving, especially earlier that week are very, very busy days. But then starting Thanksgiving, they do more blackouts for Passholders/Magic Key holders to keep the crowds from being overwhelming.
That said, the blockout levels for passes are identical on both 11/26 and 11/27 so I don’t know why there would be a big difference. I wonder if more people tend to stay home to prep for Thanksgiving on Wed and contributes to it being a little bit better than your preferred day 11/26.
What I would say is if the levels are within 2, maybe even 3 levels of each other, I wouldn’t worry about it and still go, because in the end it’s a prediction and you can make the best of even a busy day. And if you change from the preferred day in the hopes of getting lower crowds and they aren’t, then it would be all for nothing. So I would go on the day you want to go! If it’s in budget, the Lightning Lane options are a great way to maximize your time so you can get a lot of rides accomplished to have time to enjoy the ambiance/atmosphere.