Not sure this analogy/comparison makes sense? You can get to eoc in less then 3-4 years because of double xp events? The impact of double xp events is minimal except for the rich especially if you are comparing time to get to eoc. Or I could be comprehending this incorrectly which wouldn't my first time.
I've seen people gain 500+ levels in a double XP event. There are people who do all their levelling in double XP events.
For the reasons you are noting (instant finishing costs), double composing XP events will only ever gain you a fraction of one level - even for the rich.
So the real point is to look on dbl composing XP as a small gift (not on the same scale as other double XP events), and appreciate it for what it is.