>>23442856
>not only lack two cylindes for O'Neill colonies, which need 2 cylinders
You don't need to stop at two,
and technically you can remove the need for a second simply by having a second reactive-wheel spinning the other way.
Which is something you are likely to have since
- it allows to start/control the spinning without using propellant,
- it allows you to store kinetic energy for emergency.

>usually space colonies are depicted far more fragile to weapons than they ought to be
Not sure about that.
A rotating space colony is all about tensile strength, and it can be achieved in a way similar to a suspension bridge.
And you really don't want to be on a bridge that's experiencing a resonance reaction.
https://www.youtube.com/watch?v=XggxeuFDaDU
Something which I think would happen if the colony lost a whole mirror arm (if actually as heavy as portrayed), requiring to destroy the two other to balance it out.

A nuclear explosion inside a colony would make its atmosphere expand, with no way out but through the glass (3 island design) or the structure only built to resist accidental disaster.
So yes, maybe a colony built to bear the weight of a mountain wouldn't notice the explosion.
Or maybe the mountain was empty inside to avoid needing counterweight on the other side.