I remember riding the Napierville route on the Adirondack a couple of times in the '90s when the Victoria Bridge was under repair. From Rouses Point we made it to the island of Montreal in well less than an hour on track that was much smoother than the clunky CN route through St. Jean. But then we went into CP's St. Luc yard and commenced a lengthy maneuver that saw us eventually wind up in Central Station. The part from St. Luc onward more than ate up the time savings from the Napierville routing; still, we proved it was possible to go that way and wind up at Gare Centrale. It might still be quicker overall than taking the St. Jean route in its current condition.
I do think that Gare Centrale is way nicer than pre-Moynihan NYP, and certainly better than Lucien L'Allier as a place to arrive. But perhaps the latter could be improved. On my day trips from northern New York in recent years, I learned that if you get off the train at Lucien L'Allier and bear to the right inside the station, you can go through a set of doors and walk a block-long corridor to wind up in the old Windsor Station concourse, which is still a more impressive public space that the Lucien L'Allier terminal itself. I don't know who controls that space now, but lots of commuters are still walking through it on their way to other destinations.