The present perfect always has a relation to the present time, so a single sentence without further information is 'decontextualised'.
Then every tense is decontextualised as it must have a relation to the present time. By the time we use a tense, it must have a relation to the present time. It goes without saying.
It follows that every tense is plugged in the present. The twin towers collapsed in 911 is a past for example, but as we mention it now, it is plugged in to the present. Those who claim the case, in Simple Past, has no relation to the present must be out of his mind. By the way, I am sure that Simple Past "I ate dinner" can answer 'Are you hungry'.
Then the three tenses are all plugged in the present, as all are used by the present time: I eat dinner.
I have eaten dinner.
I ate dinner.
As you said, they all are decontextualised, so it is puzzling why we can use every tense to refer to the present. :(