You are quite right, the structure for radio is different than for streaming. Also, at the time, records / CD / cassette sales were significantly higher than they are now, so artist revenue from radio then was a much smaller proportion of the total than streaming is today.

What I found interesting was the precedent; the argument that radio was a means to promote artists, and therefore shouldn't pay royalties, was discounted even in those (to artists) much more favourable circumstances.