There's absolutely no question that TNG rode the wave of the popularity of TOS. But the original discussion was more about whether TOS or TNG was more popular at the time they originally aired.
TOS always struggled as a network series. It only managed to eek out three seasons, and even that was with a lot of turmoil. It was only after it left the air and went into syndication that it's popularity exploded, and then came the movies which, especially with TWOK and TVH, were blockbusters.
TNG, OTOH, was strong at the time it originally aired. It had solid ratings, it ran for seven seasons, and it was profitable and popular enough at the end of its run to warrant an immediate bump to the big screen.
My contention is not that overall, in the grand 50-year history of Star Trek
, that TNG is more popular than TOS. No question TOS wins that contest. It's the iconic one. It's the one that has endured the longest. It's the one the public still knows to this day. And, let's face it, it's the one Paramount went back to when they needed a new start for Trek.
My contention is only that at the time they originally aired
, TNG did better than TOS. And that TNG was phenomenally popular during that seven year period of time.