I think SV , ie low and slow
w/o a vac-bag is a different process resulting is an entirely different result :
Steam , in contact w the meat , is a bit like water in contact w meat : ie making a stew or soup.
the tasty bits wash off into the stock , and its the stock that makes the dish , no longer really the meat.
In the Bag , nothing is washed off. and at lower temps , the meat contacts less , so more jus and falvor remain in the meat.
my 10 cents on the differences.
after all Sous Vide means ' under vacuum '
which is a bit of a misnomer .