There is no honest one-size-fits-all answer. For a simple service on an older, out-of-warranty Lexus, a well-qualified independent shop may be appropriate. The dealership becomes more valuable as the job depends on Lexus-specific training, current diagnostic tools, model procedures, Genuine Lexus Parts, warranty authorization or a complete Lexus service record.
The most defensible comparison is the total job: correct diagnosis, parts and fluids, included inspections, written warranty, convenience, documentation and the risk of paying twice if the first repair does not solve the concern.