I dont think the Tokina is too wide for Sharks. But it mainly comes down to where and what kind of sharks your shooting. I find that any shark that is outside of the range of the 10-17mm is too far away for strobes to light up anyway. The whole idea of shooting wide is to reduce the distance between the subject and the lens for strobe coverage and fitting that subject and in the case of sharks often a large subject into the frame. Having a narrower wide zoom is more suited for strobeless shots in clear water near the surface.
I personally prefer the 8inch dome over a mini dome as it feels more balanced in the water and strobe placement is a little easier with the larger domes.
Here are some unedited, non cropped Shark shots taken with the Tokina 10-17mm on my Nikon D7000 with the Tokina mainly at 10mm