Dev Blog: The Age of Heroes Class Rebalance

False.
Drinking milk is an ongoing effort and so is balancing classes.
Why is this so, you might ask. I've already pointed out something you didn't "extrapolate just fine", perhaps I'll let you do the honor.

One inherent problem with your metaphor is that drinking milk is not a singular method to achieve the health benefits it provides; it's an alternative.
There are all sorts of other ways to gain the same benefits.
The same isn't true of balancing classes; there's only one way to put classes on equal footing.

Also, while drinking milk (or any of the alternatives) are indeed on-going efforts, class balancing does not have to be.
Done right, a large-scale balance would only need to be done once.
While minor tweaks could occur as new classes are added, there would be no need to totally revamp all classes every year.
Conversely, you can't drink five gallons of milk in one day and expect the health benefits to endure as if you were drinking your normal portion each day. That's not how the body works.

Did I extrapolate that out enough for ya?

From how I see it, MapleStory dev team has never had the intention of achieving nor maintaining the balance among their classes.
This:

is no better an assumption than anybody else's, yet is projected off as absolute truth.

They wouldn't do it if they didn't think it was worth the effort.
That's not an assumption; it's business.

As you yourself said: it costs money to rebalance all the time.