I would not agree 100% with your statement that when shooting in direct sunlight it is unusable. Try to use the quality of the lens to your advantage. This lens can produce good results if you give yourself the chance to learn how to use it.
For example these two photos demonstrate my claims above. Portraits were shot with sun behind my mom's back. Shot at Pentax K-5II and Samyang 85mm f1.4 fully opened @ f1.4 being focused through OVF. Fine tuned focus settings to -10 and relied on focus indicator in the OVF.
And the last one was shot on Pentax K-1 @ f1.4. Fined tuned focus at -8 and used OVF indicator. I can consistently get focused photos this way even at f1.4. This is basically a jpeg from a camera. I just used it to show you how consistent results can be across the cameras. I like it more on K-1 as it is easier to focus through OVF plus you have focus peaking. When you used LV with focus peaking it easier and more precise of course, but you need to hold camera in awkward position, i.e. not at your face to stabilize it, but it does the job fine. Of course I would want EVF at my eye for any manual lens but that would mean going mirrorless at this moment. Hoping for Pentax hybrid OVF/EVF very soon.