I think the New Avengers is a clever reveal in the movie itself, but I feel renaming the movie in the marketing after one week will just confuse people more than anything else. In fact, it might turn people against the movie as they will see a bunch of D-list characters and say "NOT MY AVENGERS!!"
Now to be fair, I think the movie does a terrific job of developing the characters and making you really like them. I was a bit indifferent the Black Widow movie and didn't care for The Falcon and the Winter Soldier (the two MCU properties Thunderbolts most directly follows up on with the inclusion of Yelena, Red Guardian, Valentina and John Walker). And Ghost left no impression on me in Ant-man and the Wasp. So I wasn't at all hyped to see these characters when this movie was announced, and I'm sure most people felt similarly.
Yet, by the time Thunderbolts ended, I had grown to love the characters as the movie did a fantastic job fleshing them out. So by the time the movie revealed these characters are the "New Avengers" (as the marketing is now spoiling), I was on board, and I am now looking forward to see what happens next with them. But the casual moviegoer who hasn't seen the movie yet will likely scoff at the idea of these guys becoming the next Avengers team, as they only know the characters from how they were depicted their less well received movies/TV shows.