You have to determine by interpretation what Jesus and the Apostles mean, which then becomes your own individual "ism".
For instance, you said;
Seems like the apostle Peter was of a different mindset, though.
2 Peter 3:9 The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.
You have to determine who the "any" are that God is not willing that "any should perish".
In order to do that, you have to put that passage into the context of all of Scripture pertaining to regeneration and salvation.
John 6;
37All that the Father gives Me will come to Me, and the one who comes to Me I will by no means cast out. 38For I have come down from heaven, not to do My own will, but the will of Him who sent Me. 39This is the will of the Father who sent Me, that of all He has given Me I should lose nothing, but should raise it up at the last day.
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The "any" in 2 Peter refers to those whom the Father gives the Son.
John 5;
44No one can come to Me unless the Father who sent Me draws him; and I will raise him up at the last day. 45It is written in the prophets, "And they shall all be taught by God.'[5] Therefore everyone who has heard and learned[6] from the Father comes to Me.
Once again, the "any" are those who have "heard and learned from the Father.
John 17
2"Father, the time has come. Glorify your Son, that your Son may glorify you. For you granted him authority over all people that he might give eternal life to all those you have given him.
Again, those whom the Father has given the Son are the "any" of whom none shall perish.
Interesting. I guess your 'ism' automatically relates that passage from Peter with those passages of John. I read the passages in the context of the book in which they were written and had never thought to assume such. I will study them further.
But it does raise the question of why God would be concerned about the 'elect' coming to repentance. Are they not completely 'elect' or can they be less than 'elect'?