I’m probably losing my already-limited ability to distinguish important matters from tangents, but… It’s generally agreed that Jesus spoke Aramaic, a Semitic language related to Hebrew. These languages don’t really have past and future tenses; rather, they use the perfect to indicate completed actions and the imperfect for ongoing actions. So, for example, if something had already happened in the past or was sure to happen in the future, the perfect was the verb tense of choice. If on the cross Jesus said the Aramaic equivalent of "it is finished," he probably said it in the perfect tense. So in translating Jesus’s word into Greek, John would likely have used the perfect tense, which in Greek is distinctly past. Note again that perfect/imperfect are grammatical terms, not commentaries on the excellence of the events being described by these terms.