We aren't talking about pair production ...
Yes, we are ... my claim is that because of pair production ... there is missing antimatter in the universe ...
I admire George Wald ... the man was gifted in taking complex subjects and explaining them simply ... and I'm sure the piece he wrote that you're relying on was true and correct at the time of the writing ...
50 years ago ...
We've learned a lot about the universe since then ... including that the early universe was opaque ... something George Wald (and you) didn't take into consideration ... sure,
later in the history of the universe, when it becomes transparent, we find more matter than antimatter ... my question is why? ... and the answer must come from the time before the universe was transparent, before CMB could travel freely through the universe ...
We can recreate these early conditions in the lab ... and in every experiment, we produce particles in pairs ... electrons and positrons ... protons and antiprotons ... neutron and antineutrons ... always ... one in two billion is fine until we do this 10 trillion times and always always always we produce particles in pairs ...
A short article ... give you an idea of the state-of-the-science in this "matter" ...
"Physicists Zoom in on Mysterious 'Missing' Antimatter" -- Phys.org -- Apr 4th, 2018