It is NOT too late for them to change the PVP elite set for season 4 since it has only been less than a week.
Providing last season PVP elite set than what was expected and promised, does not drive participation count which is important for inflation. This is peak lazyness from Blizzard.
Blizzard should give you a token for hitting 1800 that lets you buy any elite set for your class from season 1-3 of dragonflight, instead of you getting the season 3 set again