I think '엄청' should correspond also to several other words such as very, extremely and so on..
"엄청", despite its actual usage by native speakers, in fact means overly or excessively. You are not wrong if you're a descriptivist, but we need to follow what's standard here.
"엄청" is stricter. "너무" technically doesn't necessarily convey a negative connotation.
Once, I was in Korea, and as some of you might know, we sometimes like to just eat it raw. We just open the package, and then put in the powder and shake it up. (Doesn't really taste good when old) So then my brother was like: No, and he just dumped the whole package. And we were like bruh... ._. And it was totally inedible. So he was like: let's give it to mom. (She likes hot stuff) But that was disrespectful, because that would basically be giving it to her, as she would be a "Trash Can." This is getting too long. End of story.