While I agree with you goth that the movie isn't about being unable to escape your destiny some of the points you're making are a bit exaggerated. Certainly animal behaviors and roles play a part in TLK but on a few points for both story and Disney reasons ( keeping it PG ) they tone things down.
1. Infanticide among lions, this wouldn't have just killed Simba as they tried to in the movie but also Nala ( with one possible exception )
2. Polygamy among lions, Mufasa ( or perhaps Scar ) would have sired cubs with all available lionesses, Nala's parentage would Safarina + Mufasa/Scar.
3. Hostility of everything ( Warthogs and Meerkats included ) towards lion cubs.
All of these adjustments made a fair bit of sense to help put together the story, but it should be clear that TLK isn't purely an expression of a possible story arc for a lion.
As to the dreaming vs instincts of animals, this is also pretty exaggerated. In a literal sense big cats do
dream and there's a lot more to them then simple instincts, there's a lot of learned behavior and memory guiding their actions as well. Cats actually have superior short term memory to people and there's plenty of accounts of big cats picking up peculiar habits based off learning and accounts of them planning revenge against specific individuals. You're correct in saying they don't think like humans do but make no mistake animals
do think and process information, but how they react and process this is colored by the sort of animal they are and their individual personality.
All in all I don't think it's wrong to look for messages in TLK that have meaning in our human lives, though I agree that it's not about inevitable destiny. You might make the case that there's a message about living up to your potential and hard work in there vs being a Hakuna Matata slacker but even that's saying something fairly different about free will then the idea of inevitable destiny.