There is no such implication of extension into the future in the Greek perfect.
How about what Paul said about "extension into the future", regarding the believer's security.
Rom 8:35-39
35 Who shall separate us from the love of Christ? Shall trouble or hardship or persecution or famine or nakedness or danger or sword?
36 As it is written: “For your sake we face death all day long; we are considered as sheep to be slaughtered.”
37 No, in all these things we are more than conquerors through him who loved us.
38 For I am convinced that neither death nor life, neither angels nor demons,
neither the present nor the future, nor any powers,
39 neither height nor depth, nor anything else in all creation, will be able to separate us from the love of God that is in Christ Jesus our Lord.
There it is, in full color: "nor the future".
But, if that isn't enough evidence, how about what Jesus Himself self about the future?
John 10:28 -
I give them eternal life, and
they shall never perish; no one will snatch them out of my hand.
Here we have a very clear statement about the
CAUSE and
EFFECT of possessing eternal life.
Jesus is the CAUSE of possessing eternal life. He is the One who gives eternal life.
Never perishing is the EFFECT of possessing eternal life. Those who have been given eternal life shall never perish.
I believe in the 5th point of Calvinism, but on more solid grounds than your misunderstanding of the perfect.
Such as the above verses.