In a way you're right- Gundam was considered a "real robot" show in contrast to more magical shows like Ultraman.

But Planetes is on a different level, with accurate depictions of orbital dynamics and spacer life.

Gundam was always about societies experiencing large-scale changes that no individual person has a handle on, and the struggles of people who try to make a difference anyway. In that sense, it's comparable to The Expanse, and the "magical" elements serve more or less the same purpose.

Planetes, on the other hand, isn't much like either of these. Its subject matter is intensely personal, and even when the characters occasionally get involved in high-stakes situations, it's less to do with changes in society (which occur much more slowly) and more to do with someone turning their small-scale private difficulties into everybody else's problem. The political elements intrude for a while and disappear again, and I don't remember them nearly as well as the bits about a lost watch, or a marriage proposal.

In a nutshell, if Gundam and The Expanse need magic because they're larger-than-life, Planetes has no use for it, because it's exactly-the-same-size-as-life.