Noah,
I stumbled upon this thread while looking for an answer to the same question you had. My needs were to convert XAVC-S 1080p footage from my A7Sii to really small h.264 files so I could upload rushes of the day to my client (just for viewing purposes).
I ended up having to use an old install of Adobe Media Encoder from CS5 which did the job and reduced my 10 gigabytes of footage to 300mb (due to my extremely downsizing settings, of course).