My first watch of the series had me labeling Karli and the Smashers. Cap's speech in the final episode did make me stop and think about her and a lot of unresolved questions regarding her abilities and rise.
Aliens, Android, Wizards, in the the background. Known unknowns. Unknown Unknowns maybe unspoken threats these heroes haven't encountered.
There's something pushing the world to go back to what it was. It might only be like a tide at this point, a planetary influence correcting itself after the Snap which Captain Wilson interrupted with his speech.
While the flagsmashers are small in the worldview what they were fighting against may be so much more and so far above them and Karl's paygrade she never stood a chance to even understand it let alone fight it. Somewhere she was corrupted by even engaging it and the flagsmashers destroyed.
She's the first hero to fall.
The following series maybe deal with death too.
Loki
Black Widow
No Way Home
Marvel seems to be leading up to more heroes dying and making sure the world building makes sure they're gone. Could be wrong though, just some happy thoughts from a well of reflection.