I have the A7Riv and A6700. I also have the A6400 and several aps-c lenses. The A6700 was both an upgrade to my A6400 and an exploration of the A7Rv enhancements without spending for the A7Rv or A7CR.
There are threads and reviews which go into the details of the differences between all these Sony offerings.
It seems, to me, with my budget, with the gear I already had, etc., the A6700 was a good choice for me. At some point, maybe never, choosing between adding an a7Rv or vi?, or the A7CR or A7Crii?, would be a tough choice. "Get both!" is unlikely to be a resonable option.
I think i would suggest if budget sensitive, the A6700 and a couple of smaller aps-c or ff lenses, is clearly less expensive than the A7CR and those same lenses.
Aside from budget, the A6700 has the mechanical shutter and speed advantages.
Both the A6700 and A7CR offer the opportunity to have a nicely smaller kit when compared to the A7R family and the larger ff lenses.
Incidentally, for me, the 18-135 on an A6700 is a nicer carry than a 28-200 on an A7CR. If I anticipated 28-200 and larger most of the time, I'd probably go with the A7Rv, 20-70/4, etc., and smaller, more or most of the time, the A7CR.