Avoiding repetition can also mean structuring your writing in a way that allows you to rely on pronouns and other linguistic tools to avoid using the same word repeatedly while preserving clarity.
And I often find that technical writers don't do a good job of evaluating which terms need to be treated as rigidly defined technical terms and which ones do not, resulting in writing that it more stilted and jargon laden than necessary to communicate clearly. One benefit of taking McCarthy's advice seriously is that it will encourage you to scrutinize your decisions about when to rely on jargon and defined terms and help you identify where you're using them as a crutch to avoid harder decisions about how to write clearly.
The goal is not to be "entertaining." Rather, it is simply to should be to hold the reader's attention so you're not making huge claims on their ability to focus. I wouldn't be so quick to give up on this and embrace the "papers should be boring" mindset. The basic problem is that an extremely tedious paper does not "get your point across without doubt." It may not even get your point across at all because it pains readers to read it.
Of course, none of this should be construed to mean that people should use "thesaurus words"--i.e., words that are overly obscure or a poor fit for the situation, just for the sake of mixing it up.