Correct. The FAA is set up to be default quite conservative (small c... "Reluctant to change things without a lot of work"). This makes a lot of sense given what they do (an amortized cost to public health over decades is a lot less likely to get people fired than a private plane falling out of the sky into the middle of an elementary school because the engine failed mid-flight due to a new fuel changing the mean time between failure in an unexpected way), but it does mean that even when things are understood to be safe and proven safe, simple inertia can keep the FAA from certifying them until someone lights a damn fire under them.

Although on this specific topic, I almost wonder if you could make a case that the unleaded avgas is safer not for public health, but for the private pilot and therefore the public in terms of the FAA's main understanding of safety (IE don't let planes crash). How much is a pilot's reasoning capacity compromised by chronic lead poisoning due to the necessary handling of avgas and breathing in fumes that they must do in operation of their plane?