The power suit wiki describes it as usually not covering the entirety of the body. The power armor wiki specifically references Samus Aran as an example of a user of power_armor. However according to the Samus Aran wiki she uses a power suit, and canonically her various suit upgrades are called just that, suits.

Of Samus posts, 115 are tagged with power_suit and not power_armor, 194 are tagged with power_armor and not power_suit, and 73 are tagged with both.

Is the difference between power_suits and power_armor meaningful? Should the two tags be merged?

Samus's suit is literally called the Power Suit. As long as there is a power_suit tag, telling uploaders not to use it for Samus is a hopeless battle, because that's what they're going to assume it's for.

As for whether any tags should be merged, I'm wondering whether power_suit and exoskeleton are too similar to each other to remain individual tags. Their definitions are very similar.

I would say that Samus's power suit should be moved to power suit (metroid) and the rest of power suit should be moved to power armor or exoskeleton or other tags as appropriate. I don't think power suit is worth keeping, it's too vague and its usage is too inconsistent. In practice it's just used for random scifi armor.