I'd rather have Porcello for two years than Lynn or Cobb for 4. Not only are Lynn and Cobb both older, but both have had TJ surgery in the past two seasons. Data to date suggests TJ surgery lasts about 600 innings, so both are at risk for another surgery and missed season during a 4 year deal. Also both carry QO penalties.
So Lynn and Cobb might get you one extra season over the next four, and one fully paid season with very few IP. And cost draft picks, not helping a very depleted farm that would be needed to replace them.
And Lynn's last season appears to have been carried by some BABIP luck.
Just keep the cheaper, healthier and shorter term Porcello over these two...