Remember, grammarians examine language and then try to distill "rules". Obviously rules or guidelines cannot take into account every circumstance.
I wouldn't say personally that present perfect is mainly a present tense, but I'm sure some would disagree. How do you measure if it's "mainly" a present or past tense, anyway? Google hits? Appearances in a corpus? It's not that easy.
"Rules" typically follow use, not the other way around. In the UK I've heard that it's more common to say "Will's just gone out" whereas in the US people would more likely say "Will just went out," but we mean the same thing.
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