Hmmm, am I wrong in understanding that, by pretending leap seconds don't exist, the unix time actually represents how many seconds passed rather than what time time is now?
It's the other way around: Unix time pretends every day has exactly 86,400 seconds, and consequently, you can calculate the current time of day by taking the respective modulus.
However, this comes at the cost that the difference between two unix timestamps does not yield a duration in seconds in general.