Sorry, I have to disagree with the entire premise here.
A wide variety of experiences might lead to well-roundedness, but not to greatness, nor even goodness. By constantly switching from one thing to another you are always reaching above your comfort zone, yes, but doing so by resetting your skill and knowledge level to zero.
Mastery comes from a combination of at least several of the following:
- Knowledge
- Focus
- Relentless considered practice over a long period of time
- Detected, recovered-from failures
- Mentorship by an expert
- Always working slightly beyond your comfort/ability zone, pushing it ever forward
Imagine your proposal recast:
- Writing Achievements
- Learn a variety of languages
- Learn Chinese
- Learn French
- ...
- Experience the ins and outs of various platforms
- Write a book review
- Write a product catalog
- Write a comedic screenplay
- ...
- Enhance your understanding of the building blocks that we use as writers
- Write in the first, third person
- Write poetry
- ...
- Write in the open
- Blog
- Tweet
- Publish essays
- ...
- Teach
- Conduct a writing workshop
- Tutor students in writing
- ...
- Learn a variety of languages
These are largely the activities of beginners and students, not practitioners nor masters (or, in the case of teaching/publishing, people who should already be practitioners/masters). N.B. I am not questioning the many benefits of broadening or learning activities, just the premise that they lead to any sort of mastery.
Musicians get better by practice and tackling harder and harder pieces, not by switching instruments or genres, nor by learning more and varied easy pieces. Ditto almost every other specialty inhabited by experts or masters.
One can become a great developer in any general purpose language, in any domain, on any platform. And, most notably for the purposes of this discussion, such a developer can carry that greatness across a change in any of them. What skills then are so universally useful and transportable in software development? Two are: the ability to acquire knowledge, and the ability to solve problems.
How does one get better at acquiring knowledge and solving problems? Not by acquiring a lot of superficial knowledge nor solving a lot of trivial problems (a la your 'achievements'), but by acquiring ever deeper knowledge and solving ever harder problems.
You should take heed your phrase 'leveling up'. You don't level up by switching games all the time, but by sticking with one long enough to gain advanced skills. And, you need to be careful to recognize the actual game involved. Programming mastery has little to do with languages, paradigms, platforms, building blocks, open source, conferences etc. These things change all the time and are not fundamental. Knowledge acquisition skills allow you to grok them as needed. I'd take a developer (or even non-developer!) with deep knowledge acquisition and problem solving skills over a programmer with a smorgasbord of shallow experiences any day.
Will this lead to an as-easily-realized improvement strategy based upon boolean achievements? Probably not.