For astro stuff you rarely use the lens wide open since you want maximum sharpness (and getting focus right is a pain, so a little more DoF helps).
Same with the light trails, you will need sufficient DoF for the scene, so you will be stopped down to at least f/11 anyway. Same with landscape.
And really, most of these type of photography you are on a tripod as well.
The wider aperture of the tokina is more useful for indoor hand held work, (for indoor architecture/still life you are on a tripod stopped down). This means things like clubs, weddings. Also for some things like skateboarding is nice to go really wide but at the same time have a fast shutter speed.
So personally I don't feel the need for the extra stops on the UWA lenses. It ass no value for any of the work I do.
For me it comes down to the Sigma 8-16mm vs Canon 10-22mm. A very nice, very sharp, wider than wide very specialized tool, or a a still very wide but more versatile walkabout. With the 10-24mm type range it pairs perfectly with something like a 70-200 as a 2 lens walkabout kit. With an 8-16 (and the same goes for the Tokina 11-16mm) I would probably want to bring in something longer like a 17-55 to cover the 16-24mm end.
But it all depends on what you like to shoot. I'm just saying that for many types of photography when an ultra wide is handy you don't need a wider aperture because you are topped down to f/13 on a a tripod.