I think the point is that you only really need a wideband to get your tune done. Running it after that is basically just asking the sensor to fry and potentially piss your money away. If you tune the car right on a wideband, when you go back to a narrow-band sensor it will give you the same readings you would be getting from the wideband anyway.
Once your tune is good you shouldn’t be running outside the range that a narrowband can pick up, and if you are it will still tell you that you are way lean or way rich. If you are driving and you get one of those conditions despite your complete tune, why would the more robust information from the wideband make any difference? At that point, something is legitimately fucked up and you don’t need the wideband to tell you what’s wrong.