Desktop had this solved, on Windows there was and remains a distinction between "back" (history) and "up" (navigation).

Browsers actually used to have hierarchical navigation support, with buttons and all, back in the age of dinosaurs - all one had to do is to set up some meta tags in HTML head section to tell which URL is "prev"/"next"/"up". Alas, this has proven too difficult for web developers, who eventually even forgot web was meant for documents at all, and at some point browsers just hid/removed those buttons since no one was using them anyway.

The "Back" remains, and as 'Arainach wrote, it's only one concept and it's not, and never has been "up one level in the hierarchy".

EDIT:

The accepted/expected standard way for "take me up one level in hierarchy" on the web is for the page itself to display the hierarchy e.g. as breadcrumbs. The standard way to go to top level of the page is through a clickable logo of the page/brand. Neither of those need, or should, involve changing behavior of browser controls.