because it allows prices to reflect actual demand
I disagree that EIP 1559 makes this no longer the case! The BASEFEE continues to give readings of what the demand level is. In fact, I think EIP 1559 strengthens the extent to which observed prices reflect demand, because it solves the attack where miners manipulate observed fees by including high-gasprice transactions to themselves (as with EIP 1559 that attack becomes very costly). Plugging that hole also allows smart contracts to automatically use gasprice info, enabling eg. gas price derivatives.
Probably the one piece of information we lose is how much people are willing to pay to get their tx included 1 min earlier, but then delaying people’s transactions by 1 min is almost always a pure social waste in the first place so that doesn’t seem like too big a deal.
Maybe someone can suggest a reasonable way of approximating that from what was paid.
If you want estimates of how the demand curve works, there is this analysis from exogenous shocks to the gas limit: Estimating cryptocurrency transaction demand elasticity from natural experiments