Good work @Oliver, @TimPlumb + @Mary!
Agreed it would be nice to have a class input built-into the image edit.
We'll be adding the latest Redactor 3 in Pulse 5.1. In this the new setting imageFigure allows to turn off wrapping images with figure tag.
e.g.
$R('#content', {
imageFigure: false
});
So you could certainly use this Oliver then or just be aware as Tim says above