I have three messenger type bags: the largest Chrome (Kremlin?); the second largest Chrome (Metropolis?); and, a cotton newspaperboy bag I modified to work as a messenger bag.

I think I could take apart another bike and carry it in the largest Chrome.

I use the second largest for most of the winter.

About now, as it gets warmer, I will switch to the cotton bag.
I prefer the cotton newspaperboy bag, and I kinda grieve switching to the winter Chrome bag.
In the summer I need something that breathes and absorbs sweat; and, in the winter, I need something waterproof that will carry the kitchen sink.

I have found that if I take a minute to think about it, I can carry anything I need to carry in the Chrome Kremlin, and it balances better on my body than any of the conventional packs with which I have experimented.
Some folks say exactly the opposite; that back pack balances better than a messenger bag.

Different strokes.