And that's why, in 1973, Bob Wilson and Robert Kardashian founded Radio & Records (known colloquially in the industry as "R&R", which eventually became the dominant part of the front page logo). Its charts were format-specific and based on radio airplay rather than the external influences David references, and during its 36 years of existence was considered exponentially more useful to programmers than Billboard.
I still refer to those as a reference -- yes, there is a Whitburn book of the R&R CHR charts -- when making decisions on marginal titles.
And in fact, to acknowledge the misguided reference earlier to American Top 40 as defining a "hit", Casey Kasem used the Radio & Records charts for his countdown shows in the latter part of his career (1989-2004).