I would take every Smash character thus far in the previous engine, over a much reduced roster in a new engine.
What would you possibly gain from rebuilding the bloody thing anyway, slightly better graphics and that's it, what a bloody waste of time and money for a game of this graphical style.
All those old characters haven't just been dropped in from their previous games, all the new moves, all the old and alternative stages, the assists, the finishers, the 10,000 mechanical changes!
That sounds like a much better use of their time than rebuilding a new game engine, just because.
They way fighters interact on stages is what makes a fighting game, all those characters and stages changes up the gameplay so much, that this is more of a new game than an engine rebuild would have created.
Like I said, anyone obsessing over the term 'port' is massively missing the point. And probably had no intention of understanding it in the first place, logic is a lower priority than opinion on the good ol internet.