My attack scenario is kind of theoretical type. You can also realise bribing the miners by lending their mining power. I don't know any hardware things, aren't there other coins the miners could mine if PoW currencies go down? I've done this as an assumption in my post on stackexchange.

Hello together,

I want to discuss an attack scenario for PoW currencies using a short position. I tried to get a helpful answer on bitcoin.stackexchange.com, but there is small interest and the answers don't convince me.
I've presented the issue in

https://bitcoin.stackexchange.com/questions/63993/a-theoretical-low-cost-attack-scenario-in-pow-currencies
https://bitcoin.stackexchange.com/questions/63914/egoistic-miners-combined-with-large-transactions-destroy-pow

The main idea is lend many coins, do a large transaction and after the transaction is accepted, you do a majority attack. You profits are from double spending and your costs are the lending fee and mining costs during majority attack. I supposed that such an attack is possible if profits are higher than costs. If this is so, we can only trust transactions comparable with mining costs or we must have high lending fees. But both options show that our coin isn't an efficient currency.

Where is the fault in this consideration?