I've talked about it before, back in 1956 when the alternate rule was created (15.219) The FCC decided it was going to be a 200mw input and a 10ft antenna, but at the last moment before it was enacted they cut the limit in half making it a 100mw input limit. What had prompted the FCC to do that? - the answer is revealed in a 1964 trial against a manufacturer over their part 15 AM transmitter years prior - the issue was that it did not perform as advertised, it didn't perform very well at all and consumers were pissed about it.
But the point here is that if that manufactured part 15 transmitter in the 1950s had actually worked as well as advertised, then no investigation would have ever took place and 15.219 today would be 200mw input and 3 meter antenna.
Kind of ironic actually.
https://www.google.com/books/edition/Western_Radio_Corporation_V_Federal_Trad/JR9APKUUTOIC?hl=en
