I am user of Affinity Photo, is perfect on a macbook pro with the trackpad, but in PC the lack of a rotating feature makes me want to install photoshop as fast as possible. Also I think Krita which is open source allows that.
Rotating canvas in 15º intervals is making the software look pretty old, if I am not wrong Photoshop implemented this feature in 2007 or 2008 with CS5 or CS6.
Also when we paint in the reality we tend to rotate our paper, so not having this feature it feels pretty un natural to me. All this cool features your software has means nothing to me if you don't add a free rotation feature.
Pay attention to this please, you can bring a lot of users from photoshop (because your software is much better in other areas) if you just add this feature. People is asking for this few years ago... wake up.
Cheers.