That’s always something I’ve found interesting. The Vex we fight are basically just construction models. What are the actual combat frames like?

Yup. Surprised this hasn't been brought up during in-game dialogue.

I’ve always just chalked it up to maybe the City doesn’t know that they’re just construction units. From what I know the fact that the Vex are only construction units is brought up in the old grimoire cards that I think was from the point of view of the Vex themselves.