Threads, messages and the last post on the front page of my board? Just clutters up the front page and the info can be obtained anyway by clicking the New Posts button.
That template actually exists specifically so the admin can make changes to the CSS without touching the XenForo code directly. That template is the last one read so it will override the default XenForo CSS. You are safe to edit within extra.less. It should actually be a blank template on new installs. If it doesn't give you the desired look you can just go back in and remove the lines you added.
Last year I would have dived right into this, great learning experience but this year, COVID19 and too many complications from that no wish to do more than necessary.