Yes, you are correct, but I think the .243, in instances (bad shot selections, etc.), underpowered for deer.

Think of it this way... Your trying to kill the predator and really not worried about the meat, so blast a hole into him.
However, in my experiences, I want a clean kill on a deer, not a marginal kill, in instances mentioned...

RugerMike elaborated more on my point about not compromising shots / practice. Too many people do this when their caught up in the moment of truth. I assume everyone practices with their rifles, but many don't, and that's an issue of willingly compromising your shot (accuracy, flinch, squeeze, etc..)
Shot selection is key and then there is Murphy's law to contend with.
I wouldn't take the chance on a deer and the coyote is just going to be a maggot pie anyways!