For the public it's a relatively minor issue except where you have both high levels of traffic and low level flights of the kinds of planes that use leaded av gas. Without that combination the effect on real gas levels are minor. Ideally we have no lead emissions of course but the effects are tiny if you don't have those two factors.

Look, nobody is defending the FAA on this. GA pilots have wanted this for decades.

There was a carve out because plane engines are expensive and old (the most common engine today is a 50 year old model). Presumably it was expected that carve out would just be temporary while we worked on finding an off ramp to unleaded avgas. Nobody wanted the FAA to just ignore the problem for decades.

Pretty low. Even in the highest risk populations (children in very close proximity to piston aircraft airports), less than 5% of the body lead burden can be attributed to that source. I linked to the NIH study elsewhere in here.

It's notable, and is being banned for it. But when it's gone, it won't make any significant difference.