These guys are a pretty outstanding group of scholars. While I would hazard that the average perspective of the group is a more conservative bent, that certainly isn't true of all of them. As the letter makes clear, these scholars WANT a presentation of history that includes warts and all. The College Board's new curriculum went well beyodn that.
You can likely count on more names being added to the list as well.
While our legislature does plenty of stupid things and (whatever state legislator brought this forward) possibly could've been more nuanced in its attempt to tackle this, they are far from the only ones crying foul on this AP History curriculum and testing.