The teeth thing is just because of our high sugar, high grain diet
The first* people with bad dental health were Egyptians as they lived on bread (which packs your teeth and feeds the bacteria that ferment it and make acid) before that, and until the invention spread, people died of old age with all their teeth intact
I eat very low carb - almost entirely meat due to allergies, and haven't had a cavity since I started doing that, despite me nearly never brushing or flossing my teeth
*There were also people who lived in the tropics and ate a lot of fruit, and those with sugar cane.
Being able to make our own Vitamin C aside, the fact that a vestigial organ can randomly decide to fucking kill you is asinine from a design perspective. Its the equivalent to building a pool in the sims and removing the ladder for the first person who wanders inside.
Horses were at least marginally less ridiculous before people got involved. Not quite to the same extent as dogs, but compare a steppe horse with a thoroughbred and you'll see that they're smaller and hardier. Much better equipped to live, slightly less able to carry fully armored people on their back.
We're God's creation but God is a lazy kid that rushed the science project for the whole semester in six days and barely half assed it hoping no one digs too deep into it