They built it with a lot of drawbacks: Small modules, complex assembly, requiring modules to have their own propulsion systems, etc.

Plus, since this seems to get forgotten a lot, size matters. I find the best size comparison between the ISS and MIR is with the Space Shuttle attached: ISS [1] vs Mir [2].

[1] https://www.nasa.gov/sites/default/files/styles/full_width_f...

[2] https://apod.nasa.gov/apod/image/0210/shuttlemir_nasa_big.jp...

That's if anything an argument for a Saturn V carrying some platform that would look like the flight deck / cargo bay / Canadarm part of the Space Shuttle to orbit to help with in-orbit assembly.

Sure, you might need some such platform to construct something in orbit. That's basically a space forklift with thrusters.

It isn't an argument for Space Shuttle system as a whole, i.e. propulsion system, heat shield, solid rocket boosters & external tank, being needed.

For what it cost to launch the shuttle such a platform could have been entirely expendable with astronauts returning in capsules, and they'd still have saved money, and been able to take up 3-4x the amount of cargo up on each trip.