Discounted cash flow applies to capital like asics, but energy used for mining is instantaneous cost. When the expected revenue from mining is lower than expected power expenses mining makes zero sense.
Not necessarily, the paper itself shows motivations other than direct revenue for discovering a block (IE ability to withhold a block and selfish mining strategies).
> We also assume that miners always have space to include all available transactions.
This is also a pretty bad assumption. In reality the bitcoin mempool is almost always non-zero as bitcoin has smaller and/or less frequent blocks than many other cryptocurrencies.
