I agree that AVP doesn't need a killer app. But I think ultimately what people are asking is "why would I use this thing rather than grabbing an iPad or my Mac"
And I think the answer to that question is in the interface. I love using my iPad, but am almost always get stuck when I ever need to use more than 2-3 apps simultaneously. IE watch a YT video, take notes, and reply to slack/messages. It can be done, but it kinda sucks flipping between apps. AVP solves this by basically giving you an unlimited canvas for your iPad apps. And then it also gives you the ability to bring your mac into that iPad canvas, so you can do focused work with pro apps on the mac, while having secondary windows handled by the vision Pro. For me that is the "killer app."