Whereas Vivaldi composed works for, at most, two concerts a month, Bach had to produce a new cantata every Sunday for the service in Leipzig.
Unlike Vivaldi composing works for, at most, two concerts a month, Bach had to produce a new cantata every Sunday for the service in Leipzig.
Whereas Vivaldi composed works for, at most, two concerts a month, Bach had to produce a new cantata every Sunday for the service in Leipzig.
Unlike Vivaldi composing works for, at most, two concerts a month, Bach had to produce a new cantata every Sunday for the service in Leipzig.
The structure "whereas A did X, B did Y" is appropriate for a comparison of two actions. The structure "unlike A, B" is fine for comparing two nouns, but the GMAT does not like "unlike" + [noun] + [-ing participle] to compare actions. To compare actions, use "whereas" and a full [noun] + [verb] structure.