Brilliant timing on this thread - we don't get enough big cat discussion on here and it drives me mental.
I'm over in Leeds so obviously not your Ozarks, but the British big cat situation is basically the same deal. Massive black felid, nobody believes you, job done. We've had sightings around the moorlands here for years and the mainstream lot still write it off as ". Escaped pets". Or misidentification. Right.
What you're describing - that low, deliberate movement, the sheer size compared to a dog - that's classic. Dogs move differently. Anyone who spends time outdoors knows that.
A few questions that might help narrow it down:
Tail length and carriage? Big cats carry theirs low with a distinctive curl at the tip, Sound at all? Any low rumble or that weird coughing bark?, Time of night? Eye shine colour can actually indicate species
My honest take is the Ozarks sightings are almost certainly a remnant population of black phase mountain lions or possibly escaped/released exotic cats that have established themselves. The terrain out there is perfect - dense, remote, underexplored.
If you can get back to the same spot, set up a trail cam (Browning Strike Force is decent for the money). Even partial footage is worth something.
What was the terrain like exactly? Open field or treeline?