You are correct, but I wonder if space travel applications allow us to take certain liberties with the reactor design that are not feasible down on Earth. E.g. a simple(r) confinement design that expels the fusion products could work well in space, but is a non starter on Earth for obvious reasons.

I'm not sure how much of the design on Earth is bulky and cumbersome because it needs to be vastly safer and more complicated than what a rocket engine needs to be. Taken to the extreme, nuclear propulsion in space can be very dumb: just detonate nukes some distance behind the rocket and ride the shockwave with a pusher plate. It's a radically different design than anything we'd attempt for terrestrial applications.

Sure, but five orders of magnitude worth of liberties?

The Orion spacecraft concept you mention will use fission bombs on any vehicle we might build soon. Thermonuclear driven interstellar Orion has been proposed, but the vehicle would be enormous (and take 400 years to reach the nearest star.)