What's wrong with viewing MacRumors in portrait on iPad 6? Here's a screenshot...
View attachment 2293098
Seems perfectly fine and "nicely" usable to me.
Modern websites like MacRumors are generally "responsive" websites, adapting themselves to fit any screen size. Non-responsive websites don't adapt and can be more difficult to use on smaller screens. However, the latter is not limited to iPad Mini 6 but all screens (like iPhone too) that have (target display) resolutions below whatever the web designer chose as minimum display width. If one wants to use such sites, there is simply more side to side scrolling. If I encounter such a site and want to use it, I generally just take note and check it later when I'm in front of a desktop or laptop (size) screen.