Yeah, that Fusina port is much closer to Venice, so that is better. When we were there last week, there was already another Viking Ocean ship there. So I don't think all Viking Ocean Chioggia bound itineraries will be switched to Fusina. Yours of course will since they notified you. Fusinia is in a severely industrial area where you probably wouldn't want to be outside on the ship in that location. Pretty toxic air and soot.
When I booked my cruise, Viking planned to dock directly in Venice and changed that after booking. Honestly, I would cancel any Chioggia bound trips.
Also, honestly, one day in Venice is pretty pointless for a cruise. It is a city that requires many more days than that. Kind of like Barcelona or Rome ports. Pretty pointless to do those cities in an afternoon.