2nd level would be yourname.com.
3rd level would be yourname.site.com, like LiveJournal and Blogspot had a long time ago.
4th level would be site.com/yourname, like Myspace had a long time ago, and Facebook had after that, and Github had after that.
Once you sink all the way down to the obscure depths of 4th level, there's not much difference between site.com/yourname and site.com/whatever/yourname
Very few companies do this. Github and Twitter are some of the only ones. And they were certainly incredibly novel at the time.
Back in the 90's and 2000s, URLs looked disgusting. Remember this [1] nonsense?
[1] https://www.php.net/manual/en/session.idpassing.php (see "example 1")
That may be, but the user I responded to said "top level". Anyways, what looks disgusting about:
yourname.livejournal.com
yourname.blogspot.com
myspace.com/yourname
?
This was all before github, so objectively not novel by then.