I dont really understand what you are adding with your last post.
“My point is only that things we think are not so bad are actually worse.”
Yes absolutely! very well said. THAT is what the chafetz Chaim is telling us Lashon Hara which we are all accustomed to as the Gemara says “hakol beavak Lashan hara” is much worse than we realize. THAT is exactly what he is telling us. Not that it literally is worse than rape Obviously not that its worse to tell people someone was raped who wasnt than to actually rape her. such a contention is absurd. He is telling us that Lashon harah is worse than we realize, not that Lashon hara is worse than rape.
Nobody would have a hava amina that to get back at someone he would commit znus (a contention that doesnt really fit your paradigm so well) so so too we should treat lashon hara.
And obviously it isnt literal. since the motzi shem ra that gets an onesh is a very specific case that couldnt come up today. (We dont have naarah hamorasa’s walking around) Lashon hara never gets an onesh beis din (yes it gets tzaras but so does gassas ruach and wait for it …. gilui arayos which we learn from Paroh and SAra! Arachin 16a) By using the strict severity of punishment metric Ones gets the worst (would have to pay tzar and boshes) spreading rumors true or not , gets NO punishment listed in the Rambam’s hierarchy of determining severity. You might think (As we see in practice) that lashon hara/motzi shem ra is no big deal. So the chofetz chaim is using poetic license sayin g . NO it is horrible it like rape which you wouldn’t dream of doing , becasue we all know its horrible “יתבונן בנפשו אלו היה היצר מפתהו לילך לבית הזונות, האם היה שומע לו? בוודאי היה גוער בו: לך מעלי מלפתני בעון, שאהיה עבור זה מתועב בעיני ה׳.”
Does he say the guy says “wait I shouldnt rape because i’ll owe money” no of course he doesnt.
Another point you seem to be struggling with is that circumstances change the severity of an aveira. Not all lashon hara is the same, not all theft is the same. True Beis din treats the poor man who stole bread to feed his family the same as a rich man who stole bread out of spite., but obviously they are not the same. (as we showed from Dovid Hamelech in case you need a rayah for this obvious point,) Similarly Tazadikim are held to a higher standard eg Reuvein’s getting involved in his father’s sleeping arrangement was considered very severe, the Torah compares it to one of the gimel chamuros. For us it would barely be an aveira. what onesh is there for moving our father’s bed?
Severity is not strictly determined based on onesh. Motivation, yetzer harah, intent, and the outcome all play a role . Yes beis din isnt equipped/empowered to take all those factors into account, but don’t worry the Ribon shel olam is.