My viewpoint on this hypothetical situation...
Scenario #1: Pokemon are suddenly introduced into the world we know and love
- The world around us would be destroyed and the human race would no longer be dominant, nor at the top of the food chain.
We would live in fear of our last day on Earth taken away at the hands/paws/hooves/claws of our, now intelligent and organized, elemental overlords.
But at least we'd have fun while it happened.
Scenario #2: Pokemon have lived beside us since the dawn of life on Earth
- The environment would have time to adapt to the elemental threats it faces every day and our world may be quite different.
We would have adapted to suit our roles at the top of the evolutionary chain and rule our world alongside our Pokemon brethren.
Pokemon and humans would hone their skills and techniques in order to become the best they can be and take on anything or anyone that tries to disrupt the environmental balance.
Due to these facts, the world would be a quite peaceful place and war would never need to be waged. Common interests would bind the world's population as a whole.
Fun and merriment would be had by all and it'd be mostly like the anime without the cheesy plots/characters/voice acting.