What was Odo even doing there? He wasn't in Starfleet!
And yet it was not unheard of to find Odo manning a bridge station on the Defiant, especially when there was a Changeling related story, such as in
The Search and
The Adversary. Likewise Garak manned a bridge station several times when the ship was doing something Cardassian related. Plus, the crews have had ex-Maquis, Klingon and other species exchange officers, T'Pol, and pre-Starfleet Wesley Crusher, so leaving an option to include non-Starfleet personnel on temporary assignment seems plausible.
Incidentally, why was there a big scary monster in the koon-ut-kal-if-fee arena? That's not how it works!
- It could be a different ceremonial ritual involving fighting a beast?
- It could be from a pre-Surak-era, pre-Romulan diaspora gladiatorial games?
- Maybe someone chose a great beast as their kal-if-fee champion? The rules seem pretty arbitrary as an offworlder like Kirk was chosen.
- Maybe it's a large sapient being who volunteered to fight? We just saw its eyes.
- Maybe it's just someone's pet sehlat or some other large Vulcan creature meant to intimidate? The
Amok Time arena was Spock's ancestral lands, so if it's supposed to be the same place maybe it's another in a long line of family pet sehlats.
And why would anyone choose a hellhole like Ceti Alpha V as a place to go skydiving?
Why do people thread-the-needle on rock formations or between trees while traveling 250 mph through a canyon in a wingsuit? Why do people base jump off of buildings and bridges barely high enough to deploy a chute in time? Why do people still climb Everest despite the number of deaths? Why do people freedive down 700 feet without oxygen and risk brain damage? Why is there a 156 mile, six day ultramarathon through the Moroccan Sahara? In Trek why do they orbital skydive?
Skydiving into a raging sandstorm and surviving on the surface until you're picked up is the ultimate adrenaline rush and point of pride. Plus there's probably the novelty of it being where Khan and his people survived. It's like briefly living vicariously through the pinnacle of human physicality.