Hi Adam,
Yes, the photography board has unfortunately dwindled, although we have a relative new comer to Sony
@klmall (Kathy) to thank for keeping this forum active.
I've taken my A7r2 twice to WDW and haven't really had an issue with shooting dark rides and your A7r3 has better focus. I personally appreciate the higher resolution and DR.
The bigger question is what lenses? I used the 24mm 1.4 GM, the SZ 55mm 1.8, the 85mm 1.8 and also brought along the 105mm 1.4 Sigma, Laowa 15mm 2.0, and my Rokinon 8mm fisheye just because it's so much fun.
Hope all is well - are you still writing a blog?