I've live through both eras...

Agile, hardly any planning, write 3 times.

Waterfall, weeks of planning, write 3 times anyway.

The point is, people don't know what they want or are asking for, until it's in front of them. No system is perfect, but waterfall leads to bigger disasters.

Any real software (that delivers value over time) is constantly rewritten and that's a good thing. The question is whether the same people are rewriting it that wrote it and what percentage of that rewriting is based off of a spec or based off of feedback from elsewhere in the system.