Complex sentence: By the mid- 1730s, Lalli's career as a librettist was waning, and he was eventually superceded by Goldoni as the director of the Grimani theatres.
Split into simpler sentences: By the mid- 1730s, Lalli's career as a librettist was waning. He was eventually superceded by Goldoni as the director of the Grimani theatres.