Again, you're only talking about power. Just because you surpass your master in a few ways doesn't mean you surpass them overall. We seen Orochimaru and Jiraiya do things neither of their students could use on their own so how have they fully surpass them? You can say Sakura surpassed Tsunade with the Yin seal but can't say she surpassed her. Had Sasuke full surpassed Orochimaru he wouldn't have needed him at all but that's not the case. A new era can begin but that doesn't mean the old generation wasn't fully surpass. Give them some years and the students will full surpass all of their masters but that's not the case now. They're still 17 years old, they haven't time to increase the skills, ability, gain the wisdom, or smarts that their masters gained in their 54 years in the world.