SW was/is a great thing on its own, but Trek was HUGE, mid-Seventies.
Huh?
Star Trek wasn't even on the air, aside from reruns in syndication. There was maybe a handful of original novels, and a short-lived cartoon series, but Trek was essentially in limbo during the seventies. Even Roddenberry had moved onto other things: Genesis II, Planet Earth, The Questor Tapes, Spectre, etc.
No, it wasn't in production, but it was one of the most popular and successful shows in rerun syndication, the early conventions had huge attendance, and it was clear by that point that it was a major cultural phenomenon. No, it wasn't as big as
Star Wars became in public awareness -- but nothing in SF, or arguably in movies/TV in general, was as big.
Star Wars launched a whole new era of blockbuster films, and the popularity of pre-1977 works must be assessed on a different scale. By pre-'77 standards, taking fan culture into account rather than simply what was in production, Trek was the biggest thing in mass-media SF.
Essentially,
Star Trek was a quantum leap beyond prior screen SF in terms of its popularity and cultural impact, and
Star Wars was the next quantum leap beyond that.
.