I mean, I have no idea how many do or do not, or if there is a significant resistance to the concept across the player base.
Logically, there are going to be four groups:
1. People who follow the Adventure Day, and hate it (probably doesn't exist much in the real world, but for logical completeness there it is)
2. People who follow the Adventure Day and love it
3. People who don't follow the Adventure Day and are frustrated at the balance being out of whack and hence unhappy
4. People who don't follow the Adventure Day and ate blissfully unaware of any issues and hence happy
Now, we have no data on what percentage of the player base might plot along these lines. But if 2 and 4 predominate, WotC would have no reason to change anything.
WotC has data on player activities and satisfaction.
WotC is not changing anything about Adventure Day balance in the revision.
Ergo, I surmise that there is not likely to be a significant resistance to the Adventure Day in the player base.