What's your standard of too hot? Uncomfortably hot? From the climate I'm used to then 80F qualifies. I'm not sure 80F is any less arbitrary a threshold than 25C. Don't confuse "my personal range of comfortable temperatures goes from 0-100F" with "0-100F maps neatly to every person's preferred temperature range and therefore is an advantage to fahrenheit"
(and that's before we get into the effects of humidity, or if outdoors, windspeed, on perception of temperature)
Similarly, 0F is -18C. -18C in my country would be a minor disaster, given our historical low is -5C. Our usual yearly low is about 0C, and 0C is more logical here than 32F, with negative temperatures actually being exceptional