The issue you adressed is, as you describe in your post, not only related to noise removal. It’s the behaviour of the preview image, that doesn’t always match the output or even differs between 100% zoom and other zoom levels:
See for example:
As far as I understand the reason is hidden somewhere deep down in dt’s code and not easy to fix as it touches many different parts of the software. The solution you propose falls a bit close out of my scope but may be worth considering anyway.