You're somewhat right, but not entirely. Elliott needs to be killed in a sure-fire way, otherwise he'd just escape, and killing him isn't that easy regardless since he's protected by the world for now at least ig

. Anyway, if MC had used fictional gate, Elliott would have just swapped places with Ars again

or any other enemy who might still be on the boat. So killing them all together was his goal, but who knew there was someone within Elliott's skill range who was chilling outside the ship.
Though Lobelia could have used it right after Elliott used skill since he'd still be on cooldown, but Lobelia didn't or couldn't, and that's what the Author could have executed with more sensible plot

, maybe shouldn't even have given a handicap to Elliott's skill or show that it was only true in game, not in reality.