ok, thank you for your answers.

I now understand what happened.

Just my opinion: I have seen several 51% attacks in other coins, which finally survived.
The 51%-attack isn't the problem if the developers create a checkpoint and handle it appropriate.
And exchanges even re-enabled such coin for trade afterwards.

But the huge premine is a new problem never seen in any other coin, as much as I can remember.
The survival of AC depends on whether the devs can handle these premined coins in a approriate manner ....
We will see what the announced AC ver2 will bring to us ....