Good one. I think it's generally considered a Western in a sci-fi setting. They did try to stick to self-consistent rules and a realistic "feel" with the technology, physics, special effects and so on (no sound in space, etc) which would put it on the harder side of the spectrum perhaps. But since the sci-fi elements barely interact with the story, and so there's no deeply-considered exploration of how those sci-fi elements are consequential to the story / characters / society of that world, it could also be considered soft.

For me it’s soft sci-fi because the show was about the people. Space was just the backdrop.

Whereas something like Foundation is about the exploring the concept of psycho-history and galactic civilisations and the people are there to move that story forward.