Changing the idea of guidelines from "If following it doesn't make it worse, follow it" into "If what you have is fine, you don't need to change" would make them way laxer than they currently are, which is the opposite of what the RC rework one or two years ago was aiming to do, hence how the wording came to be like this in the first place.
In the past, guidelines were essentially just a way of saying "this can be ignored in pretty much any scenario, but is good learning material for newer mappers", and even with more serious guidelines being added, them being called "guidelines" was seen by people as being unimportant due to this (many of the current mappers and modders have kept this mindset since then). The RC rework essentially got rid of all the unimportant guidelines that didn't need to be followed and kept the ones people should actually follow in most scenarios. Because of this, changing the definition made sense, as it wouldn't obstruct creativity more than rules already do.
The definition being like it is, is mostly a way of making sure nominators can convince mappers to change bad cases in an easy way, which probably wouldn't be possible under the proposed definition. So it doesn't really matter how people do this argumentation in practice, as long as it can be enforced and done in the intended way when needed. Arguing for why keeping the current is fine is usually much easier than arguing for why making a change is bad, which is probably why so many naturally go that way. This is comparable to how people tend to want to be proven wrong rather than to have to prove themselves right, since it places the burden on the other person.
For this reason we're removing the proposed change from the pull request.
If you have an example of a guideline that, under the current definition, prevents you from doing something that is widely considered good, do bring this to us (preferably proposing a new wording in a thread here and getting feedback on that) so we can change it.