I would find real peace of mind in a design system maintained by a government that guarantees compliance with that government's accessibility requirements.
Source: I was the VA.gov engineering lead for awhile
This is just a case where folks are happy that our government isn't doing shit in Dreamweaver anymore and has moved on to something that resembles progress. However, government should be focusing on streamlining government operations, not developing accessibility standards and reinventing the same wheel. Leave that to professionals and use what's already available.
As for streamlining - this is streamlining, making it so that multiple entities within government that all need to build websites can use a common shared resource instead of duplicating the work (even "going shopping" for external solution takes valuable time).
You really ought to check out how fast this design system has iterated to date:
https://github.com/uswds/uswds/releases
> However, government should be focusing on streamlining government operations, not developing accessibility standards and reinventing the same wheel. Leave that to professionals and use what's already available.
First, I'm not sure why you think accessibility doesn't fall under streamlining government operations.
Second, the folks at USDS are top professionals from industry and are limited to a four year "tour of duty", so they aren't lifelong government employees.