Here's what's going on in Lucas's films:
First, Coruscant is fundamentally designed to evoke the Death Star. Coruscant represents the urban-political world, while the Death Star represents the pure technological world. These two worlds are conceptually distinct, yet very closely related. Coruscant does not look exactly like the Death Star all the time or at every level of its vertical structure, but there is still a visual relationship.
As you get farther from the top levels of Coruscant, where the politicians live, the aesthetic of Coruscant starts to diverge more from the Death Star, which you see in the lower entertainment levels or in the Underworld proper.
When the Empire takes over, it does not literally remodel the entire planet of Coruscant at every level and start inserting terrestrial-looking Brutalist structures into random locations, as we see in Andor. There is a very specific and unique Imperialized Brutalist look, which starts with military bases installed during the Clone Wars and would presumably have expanded outward from there as Coruscant became more and more a militarized and policed society.
There was a highly intentional system of interrelated aesthetic relationships that Lucas established across various levels of the society as well as across various time periods, and a logical progression from the Republic era to the Imperialized era was clearly being seeded by Lucas in a very specific way on Coruscant.
Andor ignores all of this, and the result is a far less coherent or interesting aesthetic universe than the one created by George Lucas, the creator of Star Wars.
I'm being told everything is supposed to look boring and dull to symbolize the Empire taking over. If only Tony Gilroy had been there to tell George Lucas what an Imperial ruled Coruscant would look like while he was working on Underworld!