The moment you make Agile about predictability you've already lost. The whole point is that there will be surprises and you can't predict everything. You don't need Agile to be predictable, but to be adaptable. And when you're more adaptable, you will make more progress but don't confuse that with being predictable.
I've been through a ton of teams, companies, and projects over the last decade. I've yet to see a team effectively size their work and create in a way that was predictable unless it was super super small bodies of work.
I've only known the teams I've worked with to adapt to the chaos of the day-to-day. I still find it fascinating that there are teams that have their shit together somewhere in the world enough to use predictability.
A thought that occurred to me while reading your insight... Indeed it's not about predictability strictly speaking. But could it be said that in some broader way there's something to it, in this more precise sense: being more predictably successful (as in increasing the chances) in achieving the outcomes we need to achieve by being adaptable and advancing incrementally?!
I disagree to this view. For many reasons. In any serious, sustainable business an answer to the question 'When will it be done?' is crucial. And while, due to the inherent uncertainty of the work, a certain answer is not possible, a probabilistic one often is. And this in turn allows one to make the right decisions in a competitive market, and it informs one about the risks taken. So, while being agile may be primarily about being able to adapt to changing conditions, being also able to forecast with reasonable certainty - for example - by when those adaptations lead to a valuable result is not just valuable in itself, it's a necessity. Perhaps unless you're going for a high risk, one-time shot or feel comfortable to build a business on luck. Perhaps. The work Dan Vacanti and others have done in this area is invaluable.