The Adjectives article in wikipedia mentions four kinds of use of adjectives; see the article for details, but (in brief) it refers to Attributive adjectives, Predicative adjectives, Absolute adjectives, and Nominal adjectives. In your example "This ruler is long", long is being used as a nominal adjective, in spite of being a relative term. Note, your question presupposes the adjectives in the examples are relative terms; that there is another object being compared to; but often the comparison is to a fixed set of things, and within that framework the comparison is absolute rather than relative.
It's a great single-word-request, word for "something that would appear to be an exaggeration or even hyperbole but turns out to be quite true."
(My brother's always doing that. "We caught a fish THIS big" (unbelievably so) ... and then he pulls out a photo of it.)
It's (now) traditional with single-word-requests to give the official answer:
Unfortunately in this casem there is no such single word.
To describe this, I tend to use phrases like "surprisingly accurate" or, "surprisingly, it was no exaggeration" or "it turned out to be literally true, not an exaggeration."
There are also phrases like "strange but true" or "unbelievable but true."
Just BTW you are perhaps using hyperbole the wrong way. I feel hyperbole is "ridiculously impossible" exaggeration. So in your example it would be like if a kid said "Our neighbourhood is so rich there are seventeen million yacht brokers!" So, when you use "millions!" that's hyperbole. ("I ate millions of calories today!") I guess, you are more talking about exaggeration. ("There are like eight yacht brokers on my street dude!" ... so, maybe really there are one or two.)
Sorry there's no "single-word" for your "SWR"!
Best Answer
(From the online OED) Antiphrasis (Rhetoric)
1533 T. More Debellacyon Salem & Bizance i. v. f. xxix, The fygure of ironye or antiphrasys.
1589 G. Puttenham Arte Eng. Poesie iii. xviii. 159 Antiphrasis, or the Broad floute..as..to [say to] a Negro..in good sooth ye are a faire one.
1650 O. Cromwell Lett. & Speeches (Carlyle) (1857) ii. 110 You are pastors, but it is by an antiphrasis, a minime pascendo.
1739 tr. C. Rollin Anc. Hist. (ed. 2) VIII. 15 He was, by antiphrasis, sirnamed Philopator.
1853 E. K. Kane U.S. Grinnell Exped. (1856) iv. 33 It was a bold antiphrasis that gave such a vernal title [Greenland] to this birth-place of icebergs.