To me, what you describe as heritage and history I would call the impact of brand. When products are similar, then brand can be the differentiating factor as to what sells. As to what a consumer/listener considers similar will depend upon the individual. ie if you find Fev really offputting, then the strength of the Fox brand will not make you listen to him.
In one sense the brand is a virtuous circle that feeds off the playlists, talent, promotions etc. Can a brand be destroyed and wounded - absolutely IMHO. Whilst Fox has the strongest brand in Melbourne (reflecting the 20 years of nurturing), I think Nova100’s has been not too shabby. KIIS - relatively worthless. Without maintenance a brand can also deteriorate - I agree that if Fox didn’t run a promotion for month they’d still be number one - but that is a short term gain with the potential for a long term fade.
I agree with your comments about current presence (as distinct from perceived presence). I think all radio stations have pared back on promotions and presence over the last decade, which probably relates to the declining fortunes of radio (IMHO) - radio has more competition and the content is not compelling, which has ultimately led to reduced advertising dollars and therefore the capacity for promotions and presence diminishes. A vicious circle, rather than a virtuous circle. So provided all the networks act in a similar manner (ie reduce costs), SCA continues to benefit from the relative strength of the Fox brand.