Personally, I think nihilistic existentialism is flawed in the sense that proponents of such philosophy are objectively viewing meaning and purpose as some "universal truth". In other words, they think the meaning in life is some definite rule or guideline. And because no such "universal truth" actually exists in reality, they subsequently impose their own subjective nihilism upon life and thus view it as meaningless and pointless.
However, I feel that the individual creates their own subjective meaning and purpose in life, whether that be believing that life is meaningful because of creation by a supreme diety (e.g. theistic existentialism), or meaning formed purely from life experiences (e.g. atheistic existentialism), or no meaning at all (e.g. nihilistic existentialism).
Meaning or purpose in life is subjective and really comes from the individual creating meaning and purpose in their life, rather than the individual searching for meaning and purpose in an objective manner.
Searching for meaning or purpose in life in an objective manner is essentially defeating the significance of human consciousness - the ability to experience reality in an absurd, self-aware manner. Why do people search for meaning or purpose as though it is some innate or forbidden secret of the universe? Meaning and purpose are merely constructs of the human mind, and therefore can only be satisfied through individual subjectivity.