The Sox might not need an ace during the season. Maybe Porcello or Buccholz emerges as the ace. Maybe we need a mid rotation guy. Or maybe we just need some BP help.
I would like to see another starter added now, but it makes sense to wait and see what the needs of the team are.
IMO, we are good enough as is to be competitive, so unless a deal presents itself that the FO is comfortable with, they do not have to make a move. They have the luxury right now of making a deal, either a free agent signing or a trade, on their terms.