Trying that for aspects which are out of the scope of science is sometimes called Scientism, too, but the people who apply science out of its scope are usually not scientists because scientists usually know the limits of their profession.
This is a key point I think, of what I would call "Scientism of the streets" and this is also what comes in my mind when talking about "Scientism". But I think there is discrepancy in the original Scientism too, but because you can argue with one hypothesis this year and with another one a few years later, argumenting the results have changed. But perhaps just your opinions have and you changed the way you constructed your research.
To answer whether an adherent of Scientism lacks the right telos and overall understanding of human existence, we would need to pick specific people and answer the question for each individual.
It seems the devil is in the details, especially when talking about something so difficult to grasp like "Scientism". I just find it interstesting, because many people of today argument with science as the backbone of there argumentation.