Personally, I don't go by score. I go by content and what's best for the user and what's most "matched" or "alike" so it reads naturally. My intention isn't to sound smug, but when writing content, I can tell when it's stilted and the same word is used over and over (both my reading and doing a count of it) vs using variations of it. Also, there's tools that I use to at least get an indication if Google might think something's up (i.e., not diverse enough).

Also, my site isn't about one topic - we have a few core things, but we sell more than 30,000 SKUs so it's easier to be more diverse, even if there are similar variations (arc flash labels, cable labels, etc.) which makes it easier.

I track my site/words in a spreadsheet so I can make sure we're not optimizing the pages for the same words and competing against ourselves.

As for backlinks, that can get a bit trickier because I have less control on how people select to link to our site. For that, I monitor and when I feel it's needed, make suggestions and/or collaborate with other sites. (Keep in mind I have 50,000+ pages.)

It's all of those. Those are all ways you seem too fake and "perfect" and it flags Google. Similar phrases (ex: labels, labeling, labeling printers, identification labels, etc.) are all more natural variations of each other that hit home the essential core message (we're know labels!) in a more natural way than having just the word "label" everywhere.