Not sure how corefeehelper computes those estimates, but I don't think it makes those estimates with the "hope" of the mempool somehow magically clearing in the next days. After all, its estimates dynamically change as the mempool size fluctuates, so I think corefeehelper publishes those estimates periodically under the assumption that the mempool size remains the same at the time of those estimates are published.
Maybe someone from corefeehelper could shed some light.
Also some wallets e.g. electrum provide an estimate themselves based on mempool size and selected fee, so maybe someone pointing to their code on computing this estimate would be also interesting.
It definitely makes its estimation with the hope that mempool somehow magically clears in the next days, yes! It's very easy to abuse bitcoin transaction fees, even with some thousands of dollars you can significantly increase the fee for everyone for a while and you know, when fees go high, people start panic and everyone pays more and more fees in order to get transactions confirmed.
Right now, corefeehelper states that 21.0 sat/byte will get your transaction confirmed in 6 hours. If I make a lot of high fee transactions and increase the baseline fee for everyone, I can pretty much stuck your transaction for more than 6 hours or probably for days, NFT ordinals are perfect example to prove that bitcoin transaction estimation at some point depends on hope.
Their logic is simple, they analyze past transactions, upcoming transactions, certain timeframes and then make an estimation.