Are you?! Let's use our common sense that the Lord gave us.
Say a righteous man has four children, a true believer. So he has four children. And he looks at his children and for no reason whatsoever he decides that two of them he hates. Two of his children he gives the best of education, the best of clothes, toys and food. He gives them his time and his love and care. Yet the two he hates get none of that. Eventually someone notices the vast difference and they call in the authorities to try and see what the issue is.
So they sit the man down and say "we noticed two of your children are flourishing. They are doing well in school, they seem to eat well, their clothes are well kept, it's clear that you care well for them. And the father beams with delight and says "Yes, I love my children". Ok they say, but you have two other children. The man nods. And they aren't doing as well. They don't do well in school at all, they look malnourished, their clothes are torn and dirty, it's clear that they are neglected. "Oh, the father says "that's because I hate them!" "Excuse me", the authorities say. "Oh yes, I hate them. I just created them to starve them and abuse them. I give them no help at all. In fact, I want them to die". "But why?" They exclaim, what have they done to deserve that abuse?!" " No reason at all. Nothing they have done. I just chose two and those are the ones I hate."
Now, don't throw Calvin at me. Don't go searching for verses. Answer this one question, "Is that a good father"? Explain how that can be considered a good person, let alone a father. Do you think authorities would allow this man to keep his children? Yet you believe that this is God. Yes, we have very different beliefs about what a good Father is. And if you had a father like that and you believe that is a good father, I feel very sorry for you.
Calvin was just a man. He was no closer to God than you or me. You say you don't believe in a pope. We agree on that point 100%. But don't make Calvin your pope. No, I don't respect that millions of Christians are under the bondage of false doctrine. The Bible never says respect false doctrine. The people, I want them to be free and to know the truth.
He didn't fail in His mission. He died for the sins of all. The fact that some don't accept His free gift doesn't mean that God failed. We fail Him, not the other way round. You say " why would someone turn down the gift of salvation?" Because they love their sin, they believe they have time, they will get saved later. That's why the Word says "now is the day of salvation". God NEVER fails, we fail Him.