How Much I've Spent on NX

I don't think the amount of money spent on NX is related to how many characters you have, or what level they are.

Let's test your theory.
In order for it to b e true the following statement must be true for you - If you had less characters, would the amount you've spent be the same?

Just because you don't spend the same amount as others per character, per level, does not mean there is no correlation between amount spent and the number of characters and cumulative level.

It just means your own amount per capita is less than someone else's.

Your true statement you seem to be trying to make is that the majority of expense compared to others wasn't from "necessities" but extras they took that you don't, but to some degree that' a matter of opinion in defining what's necessary.

In the case of an IL for example, specifically a high luck one, getting a 163 elemental staff was considered a necessity to speed up leveling, since it meant being able to 1HKO many levels earlier and therefore level that much faster - And that was only available by gaching and are one of the rarest items in some worlds.

It's a rationalization, but most of life is.