Role of Errata
Why does the Player’s Handbook errata change X and not Y?
The errata for the first printing of the Player’s Handbook sparked a number of questions. Why did we make the changes we made? Why didn’t we make other changes? Did we change certain things, such as Empowered Evocation, because they were overpowered?
The answer to such questions is straightforward: we fixed mistakes in the text. The errata fixes text that was incomplete or off the mark in the original printing of the book. In the new edition, the errata process is strictly for the correction of such things. Rebalancing and redesigning game elements is the domain of playtesting, Unearthed Arcana articles, new design, and possible revision later in the edition’s lifespan.
We play the game often, and we regularly review Twitter posts, Reddit discussions, website forums, survey results, emails, and customer service reports about the game. You have concerns about the contagion spell? We know about them. You feel the Beastmaster is underpowered? We’ve had our eye on that subclass for a while. In fact, we have a long list of things in the game that we keep an eye on and that we expect to experiment with in the months and years ahead.
But that experimentation is unrelated to errata. Corrections—that’s what errata is about. If you read the errata document and think, “We were already playing Empowered Evocation the way it appears in the errata,” then the errata process is working as intended. It’s not intended to be filled with new design surprises. It’s meant to repair spots where we forgot to tell you something, where we inadvertently told you the wrong thing, or where some of you grasped our design intent and others didn’t, as a result of the text not being clear enough.
As I have always said, and now it's in plain official text for 5th, the Errata's rule is printing/editing corrections and has nothing to do with rule updates or rebalances.
And if you're reaching for the Errata as a rules update, like this right here:
The errata amends this, saying that the spell must be of a spell level that you can prepare. (As a side note, that errata file is from June 2015, making it more current than your Twitter post).
It means you failed to read the text on the page you downloaded the Errata from. The Errata cannot trump over another rule entry that has anything to do with updates, interpretations, or balance.