I think of it as a language.
But it's not a separate language from, say, British English. That makes it a (national) dialect, itself with many subdialects.
A language is a dialect with an army and navy, so they say.
Google provides results like "dialects such as American English" from world-class linguists from the US, such as Richard Kayne.
Which idea are you grappling with?:
A: The choice of "can" vesus "could" depends on context.
B: The choice depends on general versus specific.
I am contemplating how "can do worse than V" differs from "could do worse than V." The differences between "can" and "could" are well established, but when they are couched in " ___ do worse than V" (in the relevant sense), things get murky. The meaning of an expression is not always the sum of its parts.
Only speakers who use "can do worse than V", or who can consult speakers that do in the first place, can verify whether "can do worse than V" is limited to describing general possibility. Such a requirement is necessary for the study of any dialect- or idiolect-specific phenomenon. For example, I could provide an account of how I think a particular expression is used in the Shandong variety of Mandarin, based on the meanings of its components in the standard variety. But such an account could not be taken as reliable, because I don't speak that dialect or have the opportunity to consult those who speak it.
Or are you simply saying this?:
C: "Can" is always wrong.
I might be able to share some examples that illustrate A, but I don't have anything useful to say about B (I'm not qualified) or C (I simply disagree).