In your second paragraph you said of decongestion of the mempool because of bear market. I have a question; either people are buying or selling bitcoin, there is transaction in both cases. That is to say, if people are rushing to sell off their Btc during a bear market, same congestion that is experienced during a bull market should also happen. Or am I missing anything?
What can accurately be related to bitcoin fee estimation is how congested the mempool is, because if not congested, the feerate (sat/vbyte) will be low while the feerate will be increasing as the mempool is becoming more congested. It is clear how bull market will make many other people to fomo and buy bitcoin which will lead to mempool congestion, but if no one buys again, there will be a time the mempool will not even also be congested again unlike the time when the price was continuing to increase. What I meant about the bear market is that some people will sell their bitcoin at the time, after they sell it, also people that will make bitcoin for transaction will later reduce, this will decongest the mempool.