Remember in the 90s Justice League brand had at least 4 different books going and at least 2 of them lasted beyond 50 issues and the others made it past year 1.
Also you have to consider that Justice League name get you SHELF space. Because you got some stores that won't stock a book based on its name.
See Black Lightning. DESPITE having a tv show there are stores that won't stock his book under his name. Which is why you see Batman & The Outsiders be more about him than Batman.
Its not that Shadowpact couldn't stand out-it's the amount of work to do that would be way more versus Justice League Dark.
A lot of times it snot the fans who are the issue but the stores who want to be picky.