Some animals and plants are individually stronger why is it weaker animals and plants thrive ?

I believe weaker animals and plants thrive because the weaker animals and plants tend to be smaller so they don't need the same amount of food and natural resources as a animal that is tiny like a cockroach survive because they don't have to work so hard for food and shelter. Also, if the weaker animals and plants such as producers and decomposers died out then the bigger animals such as the carnivores would have nothing to eat. Also, i think smaller animals are more durable and less confrontational and don't kill each other as much.