I think this is one of those cases, but of course, you will disagree. And that's fine, it's still a good discussion.
In Freespace, it means you lose the mission, and have to try again. In GW2, that means all the work to push back the forces have been in vain, you get a new horde re-invading your area.
The fight remained epic, but not because of movement. Sure, a fight can be epic because of movement, I don't disagree with that. I do love that GW2 has dodge etc. But a fight can be epic without movement, particularly boss movement.
Also, you're forgetting that boss fights often come with minions that the boss summons that have movement. So positioning and movement is still important for you.