That's the problem right there in the first sentence: That is how you perceived that message, "This man has the power to destroy the world!" does not translate to "This man has the power to destroy all life on the planet!" as Dream said "Folks are gonna have different perceptions on how they perceive the scale of specific feats within a title depending on what is shown and/or explained, even if they don't necessarily go along with the author's intentions." also if it was a claim of prime Whitebeard Sengoku would not have brought it up as it had no relevance to the current Whitebeard.
Yeah, exactly. We don't know what the author's intent actually was, so that's what debates are about.
It comes down to how you interpret different statements, but I generally take the low end when they are consistent with the series.
Sensui from YYH stated they must go into the demon world as the Earth can't handle so much strain, we then see earthquakes happen all over Tokyo and we see no humans being killed, even the weaker ones with Botan were fine, they just felt a huge amount of energy. Even so there are calcs to determine his power and show it was hyperbole.
The earthquakes occured because of Koenma's pacifier, not Sensui's own power. Sensui was suppressing himself the entire time on Earth.
As for the Forest of Death, again, if those are given then yes we scale from it since it wont contradict the feat anyways, however how often are those given? How do you determine Haku's speed? Or Sasuke and itachi when they were throwing the kunai? It's all speculation at that point. All pixel scaling is is finding a somewhat precise estimate of the feat on the paper. Look at Bleach characters and their speed, how would you determine that without speculating? Unless you calc it you would never even be able to determine how fast a flash step is from anyone. Again, not perfect but better than just looking at it and saying "yeah that looks more impressive so he is stronger"
If the numbers aren't given, we simply can't calc their speeds.
In bleach as you said for example, we can use peak human reactions to get a timeframe and we also have multipliers like Ichigo's bankai increasing his speed by 5-10x. We can also use the size of Las noches to determine the speed of Lanza. Then again, we have numbers given for current Ichigo.
As for Haku's speed, we have to say its below supersonic because chunin exams Sasuke (with CS1) was the first one to dodge sound.
Pixel scaling is inconsistent because a particular length can be scaled using different objects, thus giving varied numbers (one of the reasons OBD calcs keep changing from time to time). And especially for speed, since the numbers are too small and could lead to a huge variance. one example is getting timeframe of milliseconds from free fall.