- Lester worked out great and was a critical part of some very successful teams.
- Lackey gave them 3.5 fWAR and 5.8 RA-9 WAR while eating up 60 starts for 32M over a 2-year stretch.
- Zobrist gave them 8 fWAR for 56M (possibly less - I'm not sure he's even getting paid this year)
Heyward has been a worst-case scenario, as it looks like he'll end the season having provided about 6 fWAR for 76.5M (12-13M per win). I don't feel like calculating what they've paid on the aggregate for these signings, but I'm guessing it's something a bit less than 10M per win.
But I think it's worth pointing out that perpetually competitive big-market teams aren't trying to win the $/WAR title. They're trying to win actual baseball games. Cubs are probably going to go to the playoffs for the 5th consecutive year. Over that stretch they have two NLC titles and a World Series championship. They needed the wins they bought on the FA market, even if paying 10M per on the FA isn't ideal. They didn't necessarily have other means of acquiring those wins. I doubt the team or their fans are unhappy with the team's forays into free agency on the aggregate.