Depends on who you're talking to. To stakeholders? Profit for sure. To MCU fans? It's probably doing better than anything since Endgame. To those who follow box office and don't care about the movie? Could be a lot of things.
For me, I look at sequel drops for major motion pictures in order to get a metric for big success. Age of Ultron made 73% of Avengers. The Last Jedi made 66% of The Force Awakens. Rise of Skywalker made 83% of The Last Jedi (should not have dropped at all if it was a better movie). Fallen Kingdom (not well received) made 64% of Jurassic World.
So, I would hope it would at LEAST hold better than the FK->JW hold and be, at minimum, somewhere in the TLJ or AOU range of hold. That puts it at $462 million or higher.
Now, is lower than that a failure? I think that would depend on a LOT of factors-some controllable and some not. We are in a post-pandemic era. We are also in a streaming era. Movies have shorter shelf lives at theaters. That is why Doctor Strange 2 and Thor 4 had such horrible legs. Meanwhile, we have No Way Home and Shang Chi which had very strong legs DESPITE the pandemic being in full fury at the time. BUT, we know that Avatar2 will have an impact on BPWF's legs. If for no other reason, A2 will take a bunch of theaters away, particularly the higher end format screens
So, to me
Anything over $550 million is GREAT!
$500-$549 million is very very good!
$470-$499 million is slightly disappointing but overall decent (depending on OW)
$450-$469 is okay
Less than $450 million would disappoint me.
Less than $400 million would be catastrophic for the movie and the MCU in general.