no, you are wrong, the more miners the more the complexity of the network, if the complexity falls, then this is the end for POW cryptocurrencies. They become unsafe for storing coins.
There is no additional complexity when more miners arrive because the retargeting interval adjusts the difficulty back to equilibrium every 2016-block period.
It cannot fail even if most miners shut off their gear, the worst that would happen is that the remainder of the blocks in an interval become impossibly difficult to generate. Even this shut off can only happen gradually (there can be no coordinated shut down among multiple mining companies) so we would make it to the end of the retargeting interval by then and difficulty gets adjusted accordingly.
if bitcoin becomes cheaper, I have no idea what will happen to it. But most likely the developers will either change the algorithm or switch to POS
If bitcoin becomes cheaper then what I just described will happen to the network. And if blocks stall for an impractical length then you can't even make a fork to POS because without blocks being generated you can't even assign a starting activation block for it.
So I write about it, if the difficulty drops after 2016 blocks, and will continue to fall after another 10,000 blocks, for example.
In the end, the difficulty will be so low that a 51% vulnerability will appear.
nothing prevents an attacker from re-enabling many ASICs at his factory in the local network. And then connect to the network whenever he wants.
