Unless one’s definition of “long before” is in milliseconds, I just don’t find that to be the case. Say you use two rated for 2.5 amps to trip each. Now say there is a 20% tolerance and one trips at 2 amps while the other trips at 3 amps. Combined, it takes about 5 amps to trip them.
If they trip, the 2 amp unit would probably trip first and the 3 amp unit immediately sees the full 5 amps and trips immediately. That’s been my experience.