Historical Rebol did not have a notion of environments, but as I've said, Ren-C has been creeping toward them. Thanks for pointing out the similarities to R.
So long as granular bindings are permitted: I do think that contention between a binding glued onto a word or block vs. using a meaning coming from an environment turns out to be a bigger deal in practice than one might think. In part due to the fact that stray bindings happen kind of on a whim.
If you want a good explanation of a bad thing, here is how the closest thing to "global environments" used to work in R3-Alpha:
The Real Story about User and Lib Contexts
Things are improved significantly in Ren-C via "sea of words":
But still, saying "oh it has a binding already, don't use the environment" will have problems, so it will take looking through real code to see what the limits are, and where to just give up and put things in objects and refer to them via obj.x instead of trying to convince an invisible propery of which x you meant in an ambiguous case.