The question is not will they be lost, the question is will they go in the first place. People were invested heavily in the infinity saga, not so much with the multiverse saga. So will people show up for Bucky? They might, I love the character. If the perception is, who are these characters and why should I care, then it might be an issue. If the movie jumps out with fantastic reviews, it won't really matter. The marvels bombed opening week and the fact it wasn't a quality movie didn't help. I do think if it was just Captain marvel 2, it does better, even with similar quality.
Putting 2 D+ characters front and center hurt it for sure, I heard that A LOT with people I know. And based on how it did, I don't think I'm the only one who saw that. Especially with the engagement during this post endgame run. Trust me, I want this to do well. I love Bucky, Yelena and Red guardian were great. So I've got high hopes.