When brands become popular their brand names may become statistically associated with a search phrase across multiple search results.
For example, if you are optimizing for the term "This Year's Best Smart Watches", it is likely that "Apple Watch" will be statistically associated (and contextually relevant) to a majority of the search results analyzed.
Deciding how to handle these situations is more of a business decision than an SEO decision. From an SEO perspective there is a mathematically-determined contextual association with the brand name and the search term being optimized. Deciding if, and how to use it, is up to you.
Keep in mind that it is not necessary to use every term in the Semantic Index. If usage of competing brand names is problematic from a business perspective, in most cases it is still possible to achieve a B+ score or higher while omitting competing brand names -- depending on the search phrase being optimized.