After reaching Budapest on 25th, the situation did not change. However this did not affect us visiting the tourist places as most of them were open. However, when i visited Budapest again in Summer of 2018 i did notice the difference. On 25th-26th Budapest seemed like a usual city but in Summer i could see its true colours... the party place it was.
To sum up i did have a great time in Europe in December. The Christmas trees and Christmas markets open in first week of December so you don't miss much on Christmas days. However, i would suggest to make the most of your travel, plan your itenary in such a way that you avoid 24th-26th December.