Of course you can't compare car audio to a high-end stereo system built with best possible components. But a well built car system does sound awesome
( Awesome as in "hifi", not as "db-drag" kinda way). Obviously you have to do some serious modding on sound absorbtion and stuff.. Some original systems aren't that bad to begin with.
But hey, I'm just gestimating here, I don't have a highend system in my house, nor in my car