All the people piling on with "!important is evil, nuke it from orbit!" have clearly never been tasked with branding an enterprise product like SharePoint.
SharePoint's markup is rad. /s
!important isn't intended as a workaround for your own code. It's for an external asset to override an internal one.
But I'm okay with it either way. We'll still have to help people figure out where master pages / page layouts still fit in, and we will (hopefully) have an easier-to-reason-about path to use React or whatever other framework with SP in a supported way.