We had all the same arguments with the changes made in Android 12 and the monet engine as well as the combining of the wifi and cellular network toggles together into one.
These changes are derived from AOSP and with the resources of the dev team always taken up by the rapidly changing and challenging privacy and security environment, theming for obvious reasons is left as AOSP dictates it, any changes however minor would require maintenance to keep them up to date with our code base as well as relevant.
We're not an OEM with resources to focus on ensuring we have our own "skin" such as those found on OneUI, Nothing etc. also don't forget many of these companies prioritise aesthetics over security which is why you have access to patches months in advance on GraphenOS where they delay them up to 4 months. I'd rather those OEMs put their UI dept money toward their security dept instead.