Polaris, don't worry. Hitsu seems to give this advice a lot. He feels that the only way to break into the market is to be more commercial, but the truth is that you need to create a portfolio that represents the jobs you want. If you create a fluffy bunny portfolio, you'll get those kinds of jobs. If you want to get hired for dark, moody, but understated drawings in traditional media, then you better fill your portfolio with them.
You do NOT have to be a jack of all trades if you're awesome enough at what you do. That doesn't mean you don't study everything and practice going out of your comfort zone, but it sounds like you do that already.
If you want to illustrate children's books or fantasy novels or something, then take Hitsu's advice. But you can put those images in a different portfolio than this series.
As far as THIS SERIES is concerned, I reeeally like some of them. I like the concepts. Definitely something I would look for on album covers (they remind me of the cover of Deja Entendu, an album by Brand New). I wonder if you could communicate the helplessness and isolation without the text, though. I know what you're trying to do, but astronauts are a powerful image and I think you could communicate the same thing without spelling it out if you played more with compositions and lighting. Unfortunately, the images without the text aren't as strong as the ones with it (to me), which tells me that when you aren't setting a mood with text, you struggle with your theme.
I feel it's a problem of execution more than of vision. Paying more attention to your values, compositions, perspective, and rendering will help you. Your astronauts don't have to be as polished as Jeremy Geddes' astronauts, but the "sketchy" style could be done better.
'Cuz life is full of your regrets, and I should be one...