The problem with WP:PRIMARYTOPIC as written now [edit: has been modified to include "educational value" and "vital articles"] it that it mentions only quantitative factors. It is difficult to write the guideline to consider qualitative considerations in a way that doesn't make it prone to WP:GAMING, but that does not mean editors should refrain from qualitative judgements, or we could as well let a bot rename articles automatically. Popular does not always equal primary.

Note also that Titanic redirects to RMS Titanic, a good example of where precision is preferred.