I just wanted to share my experience here. During prep, I identied the different SC concepts that were being tested with the help of OG and Manhattan SC. I remember I had got a list of 25-30 different mistake categories. (unfortunately I dont have it now ). What I observed was that in problems of simple to medium difficulty, you could identify one or two mistakes on the sentence very distinctly. When faced with complex sentences, I had the same feeling as yours. Multiple concepts were tested in a single mistake. Sometimes the answer options help to identify this type of question.

As far as your prep goes, if you are able to identify such cases, you may be able to answer the question correctly.

I am beginning to notice that this overlapping of tested rules are coming up in other verbal questions. For example, in reading comprehension and critical reasoning the detail questions are the same as inference questions. A test taker can literally view the questions as the same. This is how I have boiled it down. Any suggestions?