This isn't just a Sondheim parody, it's specifically a parody of D.A. Penebaker's documentary about COMPANY (down to the producers high-tailing it to take over MGM). Sondheim is hard to parody because you've got to do music as good as his, and yet somehow the "Documentary Now!" people pulled it off. Also Mulaney's passive-aggressive performance as Sondheim is perfect. The fact that Renee Elise Goldsberry from HAMILTON co-stars is just icing on the neurotic, 1970s cake.