Leap seconds have so many problems beyond the time adjustment. It's a small/odd enough adjustment interval that there are wildly different approaches like leap smears. On top of being so small, it's rare enough (~every 2 years), depending on how a system is used, lack of proper handling might not be obviously apparent or lack of obvious problem in one implementation ignoring it may lead to lack of care in another implementation which would have a problem ignoring it.
Leap hour replaces all of that with what is more or less equivalent to a change in DST rules (except for more time zones at once). DST changes don't go perfect either by any means... but we do them regularly enough without the world crashing down that doing an additional shift change of an extra hour every 5000 years is almost certainly less hassle and breakage than the leap second approach breaking things every ~2 years.
It is way more easy to let UTC (without leap seconds) just drift away from the zero meridian and move countries to different time zones when convenient. We mess around with daylight savings time often enough that nobody will notice if we have change local time every couple of thousand years.
DST changes are pre-scheduled. Throwing a random hour in/out at (say) June 30, 2029 may be something else. Unless the jump is treated as a TZ change in tzdata?
Yeah you treat it as a time zone change where every zone moves over (or every country moves to the adjacent zone maybe). You can schedule it N years in advance. It's definitely not 0 disruption, but it's very manageable. Regions change TZs or toggle DST frequently enough that we can handle it.