No TNG was definitely a full ensemble cast. I think people say that because Data is an obvious analog of Spock. But if this analogy is to hold, who is McCoy? Riker? Crusher? It doesn't make sense.

I think they just held onto the TOS traditions of strong captain as the lead with a Spock-like character and diverse remaining cast. But TNG had more space to work with the non-lead actors than TOS did partially because it had TOS's world building as a foundation.