Let me use an baseless example of a rumor gone wrong: "Using 6 SS for E-2 Fall Event is horrible because the devs did a ninja patch that render them useless".
First of, where did that rumor come from? Then, Who put it there? Why was it there? 6 SS sounds nice but now I can't use it? When did the dev did a ninja patch? etc.
There is indeed a distinction, a less harmful rumor like "I heard Prinz only drop in node M formation 2" is still in an acceptable range as that does not stop players from doing it just destroy some hope.
But stuffs like Branching rules and Compositions are serious business. You waste time, rsc and if event comes, ships to try and do something that is based of rumor. It's even worse than doing a lottery because this one doesn't have a definite reward for doing it.
Let's say we accept this one "Rumor", what can we say to other "rumor"? If we accept one, we accept all. Then rumors that is so ludicrious will fly by and there's nothing to stop them because we accept all rumors. By the end, I won't be surprise if we have a rumor that said "You should play at Night Time JST like 01:00 while clearing E-3 for greater success because the enemy are sleeping"
Rumor is the bane of all database. If infected, render us as useless as anyone trying to explain a theory against a "it's just a dream" answer.
As I said before, if there's a definite source to provide it then it'll be a bit more acceptable, like the 30/70% thing, but the whole "lower level" thing is another issue.