I think that is likely an expectations vs reality thing where the money runs out quicker than you think. Ideally they need to bring in 2-3 SP, 2-3 position player starters, a leverage bullpen arm, and maybe fill a bench spot or two depending on how you go about doing those. The ~80ish million they likely have to spend goes pretty quick, even if you lean on Shaw/Pedro to be a full-time option, or trade from the farm to fill in a spot with an arb eligible option.
More to the point is that from a resources standpoint, more should go into pitching than the offense, so by bringing back Happ on the QO you're not only making the whole plan harder, but you're cutting off other options for filling in the other lineup slots because you need to preserve the resources for pitching. I don't think the upshot of a 2-3 win LF is worth locking that in at the outset of the offseason.