[andys627]

> Basically remove all cladding and upgrade it.

This is not extremely difficult nor expensive on every building. It's certainly more of a job than cutting holes in the wall on the inside and blowing in insulation. By insulating from the exterior you can address vapor issues. There are benefits: you can avoid having to patch holes (2 per stud bay... ie a lot) and repaint the inside. There's opportunity to upgrade electrical or fix any issues. Siding also has a limited lifetime. Wood siding can be reused.

With some/many buildings it is certainly too hard and expensive, but for many this is not. We shouldn't write off the whole idea because it doesn't apply to all buildings.