I don't think you are following this thread at all.

Large sweeping economic changes are usually bad. Medicare for all wouldn't be a sweeping change unless we immediately banned all private insurances which M4A would not do. M4A would be increasing the efficiency of the American economy which is what economists want.

Large sweeping economic changes would be things like adding $5 to the federal minimum wage all at once. The economy would likely grow from an incremental move that added $5 over the course of a few years but spiking it hard and fast will kill a lot of businesses that would have been fine with $1/yr over 5 years. It does not help to increase the minimum wage if it causes rapid widespread unemployment (note: I am absolutely not arguing against a minimum wage increase just against a rapid shift).