To Be in Chinese

I'm no expert in Mandarin Chinese, but I have taken classes with four different teachers and professors as well as studying by myself through numerous books and podcasts. This learning has taken place fairly consistently for the last ten years.

Yet a new understanding popped into my head this morning, fully formed. It pertains to the verb, 是 (shi), commonly rendered as to be. The problem with this gloss is that the English version has expanded in scope well beyond denoting equivalence of the subject and object. Let me illustrate:
1. I am working.
2. I am happy.
3. I am an American.
In the first sentence, to be functions as an auxiliary verb to the main verb, to work. The real meaning is simply an indication of present ongoing action. This is not a use of 是.
In sentence two the verb links the subject to an adjective to indicate my current state. It is implied that this is a temporary condition. We have to say something odd like, "I am a happy person" to make it a general characteristic. In Spanish there is a distinction for the usages between the verbs ser and estar, both meaning to be, but English settles for one.
This usage is easy to mistake in Mandarin. One cannot say, for example, ＂我是好" (wo shi hao). Good or well is a temporary state. It is not equivalent to me, so to be cannot link them. Instead, the sentence is simply 我好 (wo hao). 好 acts as the verb meaning to be well all by itself.
Finally, in number three we have a situation where the subject and object are equivalent. "I" is a person from the US. "An American" is a person from the US. Since they are interchangeable, to be qualifies in English or Chinese. 我是美国人 (wo shi meiguoren).