If JIRA didn't allow you to make it terrible, it wouldn't allow for some of the absurd things that people want it for and those companies might not buy it.
The saying is apocryphal and unlikely to be accurate, but the shape of the thing its describing applies to almost every piece of enterprise software whether installed on-prem or SaaS.
And as another comment points out, at Enterprise scale you can substitute "team" or "group" for customer. Every team might use a different 5%, and unless you standardize their processes, you have to buy the product that can accomodate all of their needs.
>The saying is apocryphal and unlikely to be accurate
Well its mathematically impossible to be accurate as soon as you have > 20 users.
But your statement doesn't make sense; there might be millions of features, and trillions of ways to combine them to make 5%.
It's probably in the semantics.
Text input and editing is clearly a part of functionality that's probably used by everyone (or at least most users), so it's not possible for "different 5%" to mean what you're alluding to, maybe the phrasing needs work.
In any given 5% there might be 1-4% of overlap with what others are using and the remainder of that is specific to the company.
If it's a uniform distribution of discrete features then each feature is equally "important" and worth equal resources and dev time. If 81/100 companies use the exact same 5% of features and the remaining 19 cover the remaining 95%, then all else equal you can probably drop 95% of your features and still do well.
Typically you do the most popular features first, but most Enterprise vendors end up working on a long tail of niche features that nevertheless are profitable.
There's a long conversation to be had about how this ends up being a trap where Enterprise software gets bloated and shitty and eventually gets disrupted by a small vendor that does "less," but in a powerful, transformative way that obsoletes the Enterprise "standard," which leads us back to discussing Atlassian :-)
They're a good example of this dynamic, because they have a "constellation" of products to sell. So if they build a niche feature that gets a new customer to buy Jira seats, having "landed" in the account, their salespeople can "expand" by selling OpsGenie and other related products very profitably.
However, if we assume there are, say, 100 features in Word (the real number is likely much higher), the number of combinations is orders of magnitude higher than 20.
75,287,520
+ 3,921,225
+ 161,700
+ 4,950
+ 100
------------
79,375,495