I think it is too soon to call Anthem a flop. Every big game in the looter shooter space launched with problems that led to mediocre reviews. Some of them, such as Destiny (and Diablo, if you put it in the same category), kept improving, and turned themselves into huge sellers that people played for years. That's still a possibility for Anthem.
Admittedly, there are a couple differences here though. Anthem's review scores are really bad for a big AAA release. Much worse than we saw for Destiny at launch. And, possibly even more significant, is the publisher's reputation. EA may not be as patient as Activision was. After the way they dumped Andromeda (a game in a massive, well established series, with fewer problems than Anthem seems to have), it wouldn't surprise me to see them stop speaking the word Anthem here soon. That would be sad though, as history has shown us that these games can redeem themselves, given some time.