I’d definitely accept that image quality of the Tamron lens is better than the Sony 28-60mm on land. It is great that you are testing options that we can all benefit from. The sharpness and punch of the shots are so much better than the same lens behind the dome.
What I learned when testing lenses behind the WACP, was I had to carefully check both for centre frame sharpness and edge of frame performance. With Nikon I tested lots of lenses that were better on land and thought I was going to make some great breakthrough only to actually find them worse behind the WAPC away from the centre of the frame . Many of them were sharper in centre frame and worse at the edges.
I also feel that few would want to give up the zoom. As all WWL and WACP users would comment, these lenses get used on big animals and schools of fish the most. Where the ability to zoom is perhaps the most useful feature for getting the best shot.
But most importantly, keep testing. It is very valuable to everyone, to know what options there are.