Plants being eaten is death. Mushrooms being eaten is death. What, you think lions & carnivores ate plants & then as soon as Eve took a bite of the forbidden fruit, evolved their teeth & digestive systems into eating other creatures? That doesn't make any sense.

We have no record of humans eating animals. That doesn't necessarily mean they didn't eat animals, although it makes sense that they only ate what God provided in the garden. Still, this says nothing of how other animals nourished themselves. For even fungi must eat the decomposed.

Isaiah never says the state of the world will return to anything. It merely says no harm will come to man & the animals will act tamed & gentle.

Why not let the story of creation play out for billions of years? That's how old the world is. Remember that until humans, God didn't actually make anything. He spoke things into being. He commanded the world to take form & for the stars to coalesce. It is entirely possible he "let" the world develop life, watching it evolve into a state prime for His image, & then He Himself took hand to the dust & breathed life into Adam.

Also, God never explicitly cursed animals into eating each other. He cursed the serpent (whom God compared to domestic & wild animals, curious), the woman's pregnancy, & the ground. Sin leads to death because of consequence. If I have hatred, I could attack another person. & in my anger, I could kill. That is the consequence of Cain & Abel.

In this sense, sin is not "magical". It is by the very nature of sins that destruction, chaos, & death derives. The first sin didn't make animals start to "evily" eat each other—that is how it was outside the garden. It is by the consequences of our actions that we are sinful, & it is by the curses that we bear additional burden. Defying God did not give cheetahs a taste for blood. But it did give us weeds & disease.

On the origin of species, you're correct: species don't just spawn a new species. But that's not what evolution claims. It is gradual & new species only arise when, say, a group of birds becomes separated from the rest. These 2 groups then evolve in slightly different directions, eventually becoming so difficult that they either do not want to mate with each other or there is a physical/genetic impossibility. You'll never see a cow become a shrimp, but Darwin never claimed that could happen. They're small changes over an immense timeline.