If humans never came to be, what animal would have dominated the world? Because one animal has to be at the top of the food chain... And that animal will always overproduce - no escaping it...
No! That's not how ecology works. Predator's lives are precarious. They depend on the availability of prey, who's populations vary and who move about seasonally, and any small injury that impaired a predator's hunting ability, could be fatal.
What do you mean by "dominate?" Do lions dominate hunting dogs? How about hyenas, or leopards? Why must a single predator dominate? Each specializes in a particular hunting style or prey. There may be "top" predators in some places, but none are kings.
There have been predators for hundreds of million years. They've always existed in equilibrium with their prey, otherwise they'd become extinct.
Also, would the alternate animal have been more or less environmentally healthy, considering it's appetite, and what it would have eaten. Would the food chain have been altered for the better or worse?
Alternate animal? Alternate to what?
The natural balance is always in flux; always changing to meet environmental changes.
...What about that animals waste? Would the planet be covered in feces? Because they surely wouldn't have waste management.
Seriously? When has waste ever been a problem? One creature's waste is another's treasure. Waste is food and fertilizer.
Nature functioned quite well, for several
billion years, before we came along just yesterday..