I had a job modifying them before. We actually completely removed the support bars in the middle. It does not compromise the structural integrity at all. They're only nessessary if you're filling them up with shit and stacking them up dozens of units high. You can then add walls, ceilings, and roofs that pop up out of the side of the structure, expanding the size from the initial footprint.

And if you have multiple units, you can connect and expand your living space that way. Get sick of the current layout? You can rearrange the units relatively easy, and if you ever want to move, it's a hell of a lot easier to move than a full sized house.

It's also possible to remove the toxic coating. It's not imbued into the metal.

While they're not without their downsides, that goes for every type of structure and every type of building material. Alot of the downsides you listed though are non-issues and I know this because of my own experience working on them. The biggest downsides are cost (which isn't the best indicator of viability, capitalism skews our perception of value with cost) and the fact that simply put... They're pretty fucking ugly.