The difference between Lexus and Infiniti is that Lexus has a full lineup (Sedans, Coupes, CUV's, SUV's, Hybrids, Performance). Many Lexus products are also quite different from Toyota products. And they are updated.
Infiniti's lineup is sad. They have 5 models. The QX60 is a Pathfinder in different clothes, the QX80 is an Armada in different clothes. The new QX50 has some differences but still an Altima drivetrain. The Q50/60 is unique from the Nissan lineup but is still built on a platform ( at least updated) from the G35 era. And now the new Z will appear to be built on that platform too. While, it can be just fine, I fear it will enter the market feeling old.