My basic feeling is it is possible to learn and keep Torah without being a fanatic.
But it is hard. The reason is that for every positive value there is an equal an opposite value. There is Music and anti Music. Literature and anti literature. Natural Science and pseudo science. And each anti-value tries to present itself as legitimate. So without experience and knowledge people can easily fall into cults. What makes the religious issue hard is that when one falls from holiness, he falls into unholiness, that really  bad stuff. That is not the same as falling from Rembrandt or Leonardo Da Vinci into pseudo art.

So we see why Lithuanian yeshivas are so rigid in keeping out cults and cult members. They realize how easy it is for positive value to be corrupted and fall into negative value.

Here is an idea from Steven Dutch which relates to this

The Fundamental Fallacy of Modern Philosophy might be defined as the idea that it makes sense to study structure divorced from content. This is the idea that has given us businessmen who think they can "manage" without knowing anything about what they manage, critics who claim that only the technical excellence of a work of art matters, not its content, and sociologists of science like the one with whom I corresponded who think you can study the Velikovsky affair without regard to the scientific validity of Velikovsky's ideas.

What Steven Dutch is pointing out is that content matters. Maybe external forms do also but the major issue is content, in any field. You may have heard complaints about religious fanaticism but tat totally ignores the question of what people are fanatic about. It places a Catholic nun on the same moral plane as an Islamic suicide bomber. Content matters.

And this leads to the interesting question about  a true tzadik and yet  numerous cults being formed that supposedly follow his teachings. This fact is what  causes Lithuanian yeshivas to have doubts about how to deal with this. They would like to have his books in the yeshiva because of their high value but are nervous about what they can lead to.
The higher and better something is--when it falls it falls to a more negative value.

The best approach I think is that of balance between different areas of value. And also to take one specific area to strive for excellence.  This was how my parents raised me and it makes a lot of sense to me that this is the best approach.