Of course they had no idea how their ideas would play out until they got on the air. Thats how TV tends to work. They thought it was different enough/same enough to grab the casual viewers. They wanted a TOS flavored show (or what they thought was TOS). The suits wanted a time travel element. Maybe there were too many cooks: The producers, the network and the studio. They retooled the show in the 3rd and 4th seasons in response to the lagging ratings. Though I'm in the minority, I liked seasons 1 and 2 more.The casual viewer wasn't tuning in. They were thinking, "Oh, it's just more of that Trek stuff." They had to try something that could make the casual viewer think, "Hey, what the hell is this? Looks kinda cool."Well the producers of a prequel are alway between a rock and a hard place. they can't make it too different becuse it wouldn't really be "Star Trek" , especially to the casual viewer. On the other hand if its too similar to past versions the jaded, more "sophisicated" fans get turned off.
The fact that viewership and particularly the mainstream was slipping away and tuning out shows they were doing something wrong. "Same old, same old" wasn't cutting it anymore.