The agent is able to downgrade to the $95 card (was it called Boundless?). It is just not available for new accounts. I used to have that card and the Brilliant card at the same time, but eventually gave it up for just the Brilliant. I went back to it again today. I keep my "Member since" date and credit limit.
Note that the new fee is not in effect for renewals this year. It is only for renewals in 2023 and later. However, for me, the $300 got cut significantly since the $25/moth restaurant spend is already in effect, instead of the $300 Marriott spend that I used to pay maintenance fees. Thus, I didn't want to continue the $450 fee anyhow.