"I’m aware of how all the basic settings work (my husband ... purposefully chose a slightly overexposed image to make sure you could see what I’m talking about."
That has nothing to do with how sharp the lens /camera is. Maybe how pleasing it is but not sharpness.
Let me get this 'clear', all or almost all your shoots are not real sharp. Not simply this one or just some? You do need to get another lens and another camera. This will eliminate either as the problem. Is the Siggy 35mil your only lens? Perhaps you got the kit lens with it that you can try. All you need to do is shoot the things you normally shoot using both lenses. Is one very much better than the other? Perhaps you have a neighbor that has a Rebel or other Canon camera you can try the lens on. Barring that do you have a local camera shop? They will likely let you try or even a local Best Buy. Most of these stores are pretty nice because they see you as a future customer. Maybe you even purchased your camera there?
My first impression of your shot was camera motion or shake. Was hubby moving, too, as you were walking? I am going to go watch your vids.
EB
EOS 1DX and 1D Mk IV and less lenses then before!
