Do you live or work in Zurich? Then we can meet sometime and try it. I also remembered that I used my Sigma Art 18-35 (APSC) for a while. That actually went quite well. But in the meantime I have a Sony 16-35 2.8 GM and that is really worlds better.
A very good mix of price, quality and flexibility would certainly be the 24-105 f4 which came out 3 months ago. Unfortunately it is still not available, I am waiting eagerly.

I have the Tamron 70-200mm and it works. However, the AF is very sluggish and unusable, especially in dark light or at long focal lengths. My camera is an A7RII.
I think your lens is even older, so I wouldn't rely on it being practical. However, the lens is not the best choice for an RIII anyway. The potential of the camera is lost. With Sony, especially with a 7R, you unfortunately have to bite the bullet and buy new lenses, even if they are very expensive. Otherwise, the expensive bodies are not worth it.