ubiquitin,
I think this will have to be the last time I respond, as we seem to be getting nowhere.
Steps 3 to 4 are wrong.
If the seconds are the correct length, then of course you are right that if the government decides to add 27 leap seconds, the true time of sof zman kiddush levana will read on my clock 27 seconds less than it would have.
But the seconds have changed since the new definition, and leap seconds bring them back to where they should be. This is what I mean that you have it backward.
As a concrete example, let’s say that half the molad period is exactly 1275722 seconds. If I redefine my seconds as each being 27/1275722 of a second shorter than they should be (shorter than chazal had in mind), then after 1275722 seconds as read on my clock, we will still be 27 seconds short of the zman, and on the contrary we need the extra 27 leap seconds to bring my clock reading back into line.
This is exactly what has happened with the redefinition of the second, except that instead of being redefined as shorter by a factor of 27 in 1275722, it is only shorter by 27 in about 45 years worth of seconds.
We add a leap second every time the discrepancy between atomic time and mean solar time adds up to a whole second. To reiterate, this discrepancy is caused by the fact that we have redefined the second to be somewhat less than 1/86400 of the current mean solar day (the second that chazal had in mind), and the leap second FIXES this discrepancy.
This was my second tzad. The first tzad was that chazal didn’t mean 29.5 + 793/(1080*24) of each generation’s contemporary solar day, but of their solar day always, in which case we are about three hours out.
I don’t know Rabbi Heber and I haven’t seen his sefer, but if he says what you say he says, then he is making the same mistake as you.
For your information, this is a subject that I have been interested in for many years, and what I am telling you here is not “google ben yomo”, but things that I have known for a long time.