BUT, I don't think Gene Roddenberry could carry it all by himself. I think he'd have to have some other people to make it work. A spy series doesn't seem to have been his speed. You'd want to have someone where that's in their zone.
I dunno. The '67 series prospectus document describes the intended tone of A:E as a modern-day
Have Gun, Will Travel, the series that Roddenberry wrote for the most often before his producer days (to the point that I've seen him described at its story editor, though he wasn't credited as such). It likened Seven to HGWT's Paladin, a cool, hyper-competent, rational man who comes onto the scene and uses his intellect and skills to solve people's problems. So I think he intended something very much in his "zone."
I agree that Roddenberry would've needed a good collaborator to pull it off, but not because of its genre or focus, simply because he wasn't that great a writer. As I mentioned before, I think "The Cage" is the only really good solo science fiction script he ever wrote, and the weakest of his '70s pilots,
Genesis II, was the one he wrote solo, while the strongest,
The Questor Tapes, was co-written with Gene L. Coon.
In the case of A:E, presumably Art Wallace would've been Roddenberry's main collaborator, in the equivalent role to Coon or John Meredyth Lucas in Trek. So the quality of the show would've probably come down to how good Wallace was.
TOS had allegory. With Assignment: Earth, they could've dropped the allegory and dealt with issues openly that directly effected Earth at the time, instead of using the fig-leaf of another planet. That's one advantage a series like this would've had over Star Trek.
On the contrary -- it would've been a distinct disadvantage. The whole reason that 1960s producers like Roddenberry and Rod Serling turned to science fiction was because networks and advertisers shied away from controversial subject matters, so the only way to get them on the air at all was to cloak them in SF/fantasy metaphors. When Roddenberry made his modern-day series
The Lieutenant, he famously had to fight to get the episode "To Set It Right" (with Nichelle Nichols & Don Marshall) on the air due to its story about racism. He realized it was easier to get such stories past the censors if they were allegorical instead of direct, hence his turn to science fiction. (Or at least that's how he told it after the fact. Knowing Roddenberry's tendencies to exaggerate his own biography, I sometimes suspect he was just copying Rod Serling's story.)
