Let's look at the iPhone. What made it a success? Mobile phones already existed, and the general public had a very active interest in mobile phones. The iPhone was desirable because Apple made an all-new form factor for the mobile phone, with an all-new way of using it, that offered obvious benefits over the existing products on the market.
With the AVP, VR headsets already exist. They already do essentially the same thing that AVP does. The form factor is essentially the same. In fact, in some ways, the AVP is more limited in functionality than competing headsets. Apple has barely moved the needle. Whatever they try to do in the future is irrelevant to the AVP, because it has contributed so little to whatever may or may not be a sucess in the future.
I don't think the iPhone is a good reference point here as it was indeed, as you state, a ground breaking product that did not have direct competition at launch. Probably better examples would be the iPod and the Apple Watch which were in no way the first to market for what they did, like the AVP.
So why did both those products become so ubiquitous and blow away all competition? Well with the iPod it was a combination of compelling industrial design, decent and usable software (certainly relative to their competitors) great marketing and relentless iteration to hone the product to suit the required user cases of the market.
The watch was a harder sell in many ways as it was initially totally dependant on the phone which many people had gotten into the habit of using to find out the time anyway - and telling the time was basically the most essential purpose of the watch. Even the marketing was not right at the beginning as they struggled to find an angle for it, pitching it as a high-fashion accessory before in time settling it on being a fitness orientated thing. But still there was compelling industrial design, decent and usable software (relative to competitors) and relentless iteration to hone the product.
So transpose this to the AVP. The industrial design is not right yet as it's too heavy but we know there will be relentless iteration that will improve the wearability of it - the ultimate aim is a glasses product after all. There's good software and distinct experiences that sets it aside from other AR/VR products and I have no doubt marketing will find the best position to take to best sell its worth to consumers.
The one thing that does separate the AVP from the watch and the iPod is of course price, but we can be sure there will be cheaper versions to come and gradually as they iterate, make the product more wearable for longer periods, provide more content and other reasons to use it and make it more affordable and thus more mass market, so we might eventually see what the ultimate end goal looks like.
Now that end result might still be too compromised for some, or not serve a useful purpose for others, or might still be too expensive for many - if that comes to pass then sure, you can label the whole project a flop. But this is a long road to go down before we get to any sort of realistic point when someone can state whether it's a success or a failure. To call it a failure so after just 6 months of commercial availability is crass and does not even start to take into account the technologies developed for the AVP that will filter down into other Apple products - much as F1 benefits car manufacturers as a technical R&D medium as much as simply a competitive sport.