If no matter when the rapid is taken, it's gonna be negative because I must've been contagiousness before/after, then your whole premise is a farce. If a theory can't be proven false, it can't be proven true either and deserves no discussion.
If peak contagiousness is before symptoms, and rapids are negative when not contagious, hardly anyone you know would ever test positive on a rapid. I'm just not buying it, sounds like complete BS to me.
Every test is only indicative of the time it was taken. That is well established.
Peak transmission is before symptom onset, that is also well established.
People can be PCR positive and not contagious, that is well established.
When people are PCT positive and antigen negative, they have lower viral loads, is pretty well established as well.
Which part do you 'think is BS'?
The use case for rapids is to screen people who may be contagious even if they don't present symptoms, such as travellers, people exposed to covid cases, or just screening general population before large gatherings or VIP meetings.