Yep, indoor is much safer and healthier for the cats. It's not like cats have goals and ambitions out in the big wide world. They spend most of their time laying around and doing that on a couch vs under a bush is only meaningfully different in that one location comes with a much higher risk of parasites and being eaten.

Not to mention that it is much easier to monitor the health of indoor cats. Tracking weight, litter box usage, and food and water intake can easily add years to the life of a cat. Though, outdoor cats probably need to worry more about cars and bobcats than kidney disease.