As a third generation protocol geek, I wish authentication had gotten baked in a bit better. But, as you point out, we didn't have PKC in the toolbox at the right time.
As for general symmetric encryption, it was certainly one part horsepower (even now), but it was also that crypto just makes fragile things even more so. I mean, it took years before TCP stack were hardened enough to not blow up on their own, much less when you added crypto
