That would be incorrect. Sir Robin is an elementary spaceship, but it is not period-4, and certainly much larger.
With "... the other standard spaceships,..." instead, I think that would become technically correct. But the main question "why this is interesting?" remains. If you are putting this in a DYK item, you're basically asking a question to the LifeWiki reader:
"Did you know that mold and mazing, the smallest period 4 oscillators, are smaller than the heavyweight spaceship but larger than the other standard spaceships, which are all also period 4?"
Now, why would a LifeWiki reader even want to know that particular piece of information? I don't see how it is particularly interesting. I think it is an arbitrary comparison (perhaps arising from an initial error when some editor mistakenly believed that HWSS is smaller than mold and mazing).
TL,DR: I object to the suggestion to add this arbitrary complicated comparison between some p4 oscillators and some p4 spaceships as a DYK item.