The only thing I would say is that if you are going to use a lightweight road bike for commuting, and you are going to mount a rack, beware using a seatpost rack. Over time, the pressure and stress can fatigue the seatpost and cause it to crack.

I have firsthand experience with this. Since I don't have any other reliable way to mount a rack, I replaced my seatpost with an old-fashioned heavy-duty seatpost from an old Schwinn Super Sport. I hope it fares better--I think it will.

Periodic inspection of your seatpost in this case might be a good idea.

Other than that, you can use a backpack. In that case, any bike can be used for commuting, just don't subject you bike to any kind of riding you wouldn't normally use it for, like riding through dirt, gravel, etc.