You have to keep learning - That's right slow down for even a year and you can be left behind in consulting.
That's not what this means.
You're not being brought in for your knowledge of new tech X. You're there because you've demonstrated that you're smart.
They know that they can drop you in sideways to a broken project in an unfamiliar stack, with confidence that you'll be committing code the first day.
That's where the "learning new things" comes is. Fast, and on the fly.