None of the spin-offs launched a franchise. And barely a year after NBC cancelled the show they tried (and tried repeatedly) to get it back until Paramount condescended to an animated production."The Cage" sold TOS as a concept, but not as a series. WNMHGB did sell it as a series and it was a very strong pilot followed by a season that was not only TOS' best but arguably the best and strongest season overall in the entire franchise.
"Taking awhile to get its legs" simply doesn't apply to TOS. In terms of storytelling it was solid and competent from the get-go.
You really can't include TOS in the conversations referring to the spin-offs. By the standards the spin-offs are held to TOS was a failure.
And, yes, you can include TOS. The assertion that had been made was that all Trek series took awhile to get their legs. And that assertion is false.
STNG directly launched the franchise. TOS indirectly.