How come such a "strong" expression as なるほど is used in such a "soft" meaning?

Question

Usually ほど is used to refer to some degree/extend that is in some way high, or even approaching/reaching some upper limit.

Given how precise(※) and reserved Japanese usually is, I find it surprising how「なるほど」 is used as a casual(＊) interjection meaning "I see.". I would rather have expected it be sound overly confident, in the sense of "I see/understand/... it now crystal clearly".

Looking at the etymology from gogon-allguide (and other sites):

なるほどがこのような意味に変化したのは、「できる限り」という程度・状態はそれ以上のものがなく、「他には考えられない」「明らかである」の意味に通じることからと考えられる。

unfortunately doesn't really answer my question.

Am I fundamentally misunderstanding the meaning of ほど here, or is なるほど simply an overstatement? How come that this is used so casually(＊), where Japanese is usually so precise in it's statements(※)?

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(※): Since this seems to be misunderstood, here's an elaboration:
I mean precise in the sense of accurate, not in the sense of definite. So for example when one does not necessarily know something exactly, or does not want to express too much confidence, it is common in Japanese to in some way express that (等・くらい・みたい・よう・そう・…), instead of making a definite statement that might not be correct.
While this at times is purely used for politeness, the sentiments of statements never overstepping what one actually knows seems to be common throughout the language.
And in that vein, my wondering about はるほど originates.

(＊): I do not mean casual in the sense of casual Japanese (in opposition to polite, or literal Japanese), but rather casually, in the sense of using it without much thought or meaning behind it, as an interjection in a conversation to respond to the other's statements without really saying much (besides "I follow/understand/... what you are saying" or "This information is new/interesting/...").

Answer 1

This answer is written as a supplement to Naruto's answer and a response to some of your comments on that answer. To put it simply, I think you are expecting an unrealistic level of systematicity from semantic drift. The ways that the meanings of words change over time is very hard to predict, and can be influenced by any number of things.

Assuming that English is your native language, I would for example point out that the current usage of bless you as a response to someone sneezing is bizarre. Handing out divine blessings for every sneeze seems pretty strange to me. Similarly, ballpark at some point became viable as a verb meaning "to roughly estimate". There is always a reasonable history behind these changes (whether we know them for certain or not), but I don't think we can expect them to be systematic. Once なるほど crystallized as an expression, it's hard to say why it changed the way it did.

Finally, I think generalizations about languages - like that Japanese is precise - are pretty tricky things. It's true that Japanese uses a lot of ぐらい・など・〜そう etc. to express indefiniteness in statements, but English expresses a similar kind of indefiniteness with verbs. Statements like it seems that, we found that, results show that are all arguably ways of avoiding apparent statements of fact, among other things. The fact that Japanese is infamous for requiring context to comprehend/translate because of its tendency to omit subjects, objects, or other things, could also make a pretty strong argument for it being an imprecise language. This all gets very subjective very quickly.

Answer 2

Have you ever learned classical Japanese? As is the case with other languages, the meanings of many Japanese words have changed drastically over time. For example, 貴様 was a honorific word in the past, as the two kanji suggest, but it is a fairly rude and rough word now. The meanings of the components of a word can be forgotten. (See this and this for examples in English.) Such a process is common in any language, and I don't think なるほど is special in this regard.

That being said, なるほど is not simple "I see", either. It sounds a little stilted and pompous even today, and it may be related to its etymology. In casual settings, なるほど is not really common.