While 6% -> 4% doesn't sound like a lot, in terms of revenue it has a big impact.

The peak of DAI outstanding in June-July 2022 looks a bit suspicious. Like if it was driven by market dynamics (post Luna collapse) Especially compared to the previous peak, which looks a bit more organic, or driven by ETH price.
Here’s ETH price during 2021:


This seems like ETH price being the main driver of DAI minted, with DAI mints lagging.
ETH-B maxxed during first peak in May 2021, but the next bullrun lead to more DAI minted.

In fact it's almost 1:1 with ETH
- ETH: 2k in July 2021 and 4,8k in November
- DAI outstanding: 60M in July and 180M in November

Could we get the DAI outstanding chart with the y-Axis denominated in ETH. (Converting the outstanding DAI on day x to ETH on that day just for viz)

During June 2021 to Nov 2021 was the time of “organic” growth of DAI outstanding, but we don't see a lot of whales depositing. The most important marginal DAI minter is probably someone with a decent amount of ETH, looking for some stables to play with, but not a whale.

We can see in the vizualizations that as ETH price rises people hypothecate their precious coins.

To sum it up: If we could get DAI outstanding priced in ETH at that day and avg vault age per day historically, that would be interesting.
The current viz suggest that ETH price is driver #1 and fees should be set for maximum value extraction. In times of ETH dumps MOMC could experiment with lowering fees to keep vault users. But the reality of a market panic means people will repay to avoid liquidations, no matter what fees do, most likely