Learning is not a zero-sum game.
Learning about statistics does not mean that you can't, or won't, learn Python or R. Learning about C++ does not mean you can't, or won't, learn about 3D modeling.
In fact, learning one thing often makes it easier to learn other things, even if they seem unrelated at first. For example, maybe somebody with a background in statistics can learn more about Python using a statistics library. Or maybe somebody who knows C++ can learn about 3D modeling by importing their models into a graphical engine.
All of these things are tools, just like a hammer or a saw. A carpenter doesn't learn about a saw instead of learning about a hammer. They learn about both, and part of their expertise is knowing when to use each.
In big data or machine learning, I need to know statistics, but will I use it more than python and/or R?
It completely depends on the specific role. There are some machine learning roles that are more statistics than programming. There are other machine learning roles that are more programming than statistics.
In Virtual Reality or Video Games I need to know Unity and there's a lot of 3D in it, so, will I do modeling in 3D more than programming on C++?
It completely depends on the specific role. There are some game development roles that are more 3D modeling than software development. There are other game development roles that are entirely software development.
You've cherry-picked a few examples of some skills you might need in some of these roles, but it's a false dichotomy. Machine learning requires people from many different backgrounds: programming, statistics, ethics, management, customer support, API development, etc. Game development requires artists, programmers, level designers, sound engineers, writers, colorists, etc. Not every game is made in Unity. Not every game is 3D.
So, do what you enjoy the most, and stop worrying about it. I'll repeat the advice I just gave in this question:
Give yourself an achievable goal. The goal should be fun and interesting to you, and it should be achievable in a reasonable amount of time. A single weekend is a good starting point. Finish that goal, and then iterate. Explore topics that you're interested in, but do it with short achievable steps.