As Mistu4u points out, understanding the temporal reference of the simple sentence Mario had come home, in the past perfect, requires a context incorporating a past Reference time to which the Event time can be related.
However, you are mistaken in believing that this is not equally true of the simple sentence Mario has come home, in the present perfect.
To be sure, the present perfect tells you that Reference time is the same as Speech time, the time at which the sentence is uttered. But the bare present perfect sentence tells you no more about when the Reference time occurred than does the bare past perfect sentence. In both sentences, the tense constructions tell you the same thing: the relative temporal positions of Speech, Reference and Event times. In both sentences, you require additional context to understand how these three relate to the time at which you encounter the sentence.
That context may be provided by the immediate situation —if, for instance, the sentence is spoken in your hearing and you have reason to believe that speaker is narrating a present fact and not quoting another’s past speech. It may be provided by a date on an email or letter. It may be provided in the surrounding discourse, whether a conversation or a historical monograph or a work of fiction.
But both sentences require context to provide any more information than the relative temporal positions of the three syntactic times.