The biggest difference is that after 64 they went to machines doing most of the work. Prior to that there was alot of hand fitting of parts.Winchester could not keep up with Rem while having to pay all the skilled laborers. Also they went to impressed checkering done by machines instead of hand cut checkering, again having to pay skilled laborers.
As far as the new ones I guess machines are better now and tolerances are tighter so it made it feasable to bring back controlled feed. Also market forces made it economically wise.
The pre'64 M-70 was controlled feed, by skilled laborers using Bridgeport milling machines to mill the parts. The new M-70 might be push-feed, controlled feed, or a kind of combination controlled feed / push feed, depending on the exact model, caliber, and so forth.
Is one better than the other? That's subjective. But I'd say that we have manufacturing technoligies that can take out a lot of human error and these technologies -namely computer numerically controlled machining- didn't exist in 1936.