As of now, you can complete all content in the game without using world buffs. It's totally doable so long as you meet the gear requirements as a raid and use consumables and follow mechanics. World buffs purely exist to cut down on time and increase your maximum hits. If your raid is relying on world buffs to kill a boss period, then you're not prepared for it to begin with and that's just taking shortcuts.
The point to getting 60 is that BWL and all further raids require you to be level 60 to enter. And most raid gear past MC requires level 60 to equip. The point is also to go and focus on getting your pre-raid gear before you step into an instance so you're at least prepared to upgrade those slots to the next step. And I don't mean upgrade that you strictly need those items to get the next ones, but that it shows the other people in the raid that you aren't just there straight fresh 60 looking for a gear handout.