Sometimes things get trapped in a local minima. Particularly when a seemingly inconsequential detail at a much much earlier stage becomes a dependency of lots of downstream stuff, but then it turns out that this just so happens to conflict with a better option in the here and now.
More commonly, the "perfect" solution is extremely brittle while the (supposedly) "good enough" solution is incredibly robust to all sorts of environmentally inflicted bullshit. In other words, most of the time evolution is practical while the humans criticizing the outcome are ignorant idealists.
Anyway, the example I was thinking of is here: https://en.wikipedia.org/wiki/Diffusion-limited_enzyme where some enzymes have evolved to reach extremely close to the maximum rate of catalysis limited by diffusion rates (and some enzymes have clever tricks to get around that).
That's it: and it's separate from good enough because that can include things like "happened to live on the part of the island which didn't get obliterated by a volcanic eruption at the only point in history that volcano ever erupted".
Koalas biggest problem is us? Like they seem perfectly adapted to their niche. Eat lots of leaves that nobody else is adapted to use as food, and once a year, run very fast to outpace the bushfire that your principle food source needs to reproduce.
In my defense, domestication is still technically an evolutionary process.
This was believed in the 20th century, but we now believe the appendix is actually useful, and is basically a fail-safe in case the intestinal flora are wiped out; some will survive in the appendix and repopulate the intestine.
> gut fauna
May I be excused? My macrophages are full of slime molds!
It's called "gastrointestinal illness". From the article I linked:
"Research in 2012 reported that individuals without an appendix were twice as likely to have a recurrence of Clostridioides difficile colitis. The appendix, therefore, may act as a reservoir for beneficial bacteria. This reservoir could repopulate the gut flora following a bout of gastrointestinal illness."
Remember that cephalopod brains are donut shaped and their digestive tracts go right through the middle and if they eat something too big they'll have an anyeurism. Pandas and koalas evolved special diets that serve no evolutionary purpose and both would be extinct if humans didn't find them cute. Sloths have to climb down from trees to take a shit. Female hyenas give birth through a pseudopenis that often ruptures and kils them. Horses can't vomit and if they swallow something toxic, their stomach ruptures. Also their hooves and ankles are extremely weak and not well designed to support their weight. Numerous species like the fiddler crab and peacock have evolved sexual displays that are actively harmful to their survival.
And as for humans, our spines are not well adapted for walking upright, our retinas are wired backwards, and we still have a useless appendix and wisdom teeth. The recurrent laryngeal nerve has an unnecessarily long and complex route branching off the vagus and travelling around the aorta before running back up to the larynx.
Evolution is not smart. Evolution isn't even stupid. It isn't trying to keep you alive and it isn't even capable of caring if you die. Yes we should absolutely fuck with it, because we don't want to live in a world where we still die of sepsis and parasites and plagues because "we don't want to mess with evolution."