I don't see it that way. I see it as highly anticipated, heavily promoted, but not an "unqualified hit." Out of the gate, it was a huge unknown, with an uncertain future - even the actors knew that.
It was a big, high profile gamble. That's why the debut numbers were so high. There were many questions swirling around it, many doubts, many questions.
TNG stumbled, soared and fell through its first two seasons; it became a hit in its third season, as it found its own footing, came out of the writer's strike-affected second season, and outlived its predecessor.
You just don't want to be wrong, but the numbers simply state that you are (unless you can produce something that says differently). You don't renew the most expensive series, which is millions of dollars over budget at that point according to the documentary, on TV six to eight weeks into its first season unless it is pulling in exceptional numbers.
Just because the first two seasons aren't up to your standards doesn't mean the series wasn't pulling good numbers every week. Hell the article I quoted said some network stations decided to leave TNG in primetime over network offerings.
I'm a huge TOS guy, but that doesn't change the fact that TNG was pulling great ratings right from the beginning.