i don't think that's the point anybody is making. "good lawyers" is not the profession at risk here. a top tier courtroom lawyer won't be replaced by AI.

but how much of the revenue of the average law firm comes from that, vs the day-to-day "we need this relatively routine contract reviewed" sort of work?

Former attorney here. A good paralegal is worth 3-4 junior attorneys. A good paralegal with AI should probably still have a senior attorney oversee them but this will absolutely hollow out firms.