he refused three times to heal a little girl because her mother was a Canaanite (Matthew 15:22-28)

Three is a symbolic number in the Bible. He was testing her faith, as happens quite often throughout the entire Bible, and she was rewarded for her persistence, because it proved she actually had faith in Him and wasn't just hoping for a miracle.

he cursed a fig tree to die because it wasn't the season for figs and he had a tantrum

Contrary to what a lot of people believe, Jesus was actually a human with human traits. He was hungry, he saw what he thought from a distance was food, and when he got there, he saw that he'd been duped by an early-blooming tree. He got annoyed and said "I hope you never produce fruit again." Same as you telling the nightstand to screw itself when you stub your toe in the middle of the night. Doesn't make you a terrible person.

he himself said that he did not come for the gentiles (Matthew 15:24)

Part of the first example you mentioned, so I'm not sure why you put it separately here.

Matthew 5:18 Jesus says that not one tiny element of the Judaic law will be undone before the end of the Earth

Taken out of context. If you read the chapter, the stipulations he gives for people to actually be completely right in the eyes of the law are quite literally impossible. He also says (I think a verse after what you reference) that you must be holier than the Pharisees to enter Heaven. Considering Jesus really did not like the Pharisees (called them a bunch of hypocrites), it seems to be there's some tongue-in-cheek action going on throughout that passage. The point of that passage, to me at least, is to show that literally no one can or will be perfect. Everyone makes mistakes, and the idea is to try to uphold the law to the best of your ability, not to diminish the law and say "oh well, that doesn't matter."

I'm not a Biblical scholar, and granted pretty much the whole thing is open to interpretation, but I don't really see how any of what you quoted can be used to say that Jesus was a terrible person. Also, I like that little tangent about Paul there at the end. Very related.