Well, since the ST universe has some fundamental differences from our own in terms of physics, biology, and astrocartography, there's really no point in trying to rationalize it as a timeline branched off of our own. Ultimately, it's fictional, we're not (at least as far as we know). It's just a question of whether you want to make the fictional history look generally familiar to the audience to ease their suspension of disbelief.
It's certainly a balancing act to make the fictional environment credible by creating a fictional history that audiences find familiar and dating the material or making creative decisions that will make it seem quaint when it is viewed years later.