Lynn and Cobb appear to be the front runners for Mets fans wish lists and both are good pitchers. The question, and the hard part, is how good and how much to pay for them?
A bona fide contender (Astros, Cubs, Dodgers, etc.) in need of one piece will overpay with a lack of other options, even if neither is a TOR pitcher.
A team in need of pitching will overpay if the pitching is the difference between contending and not (Brewers, Angels, Rockies).
The team that has multiple question marks across the board is not a team that should overpay and frankly only pounce if the cost is a gift. The Mets are, imo, that type of team. If all things break right and they are contenders in July....that is the time to pay.
To consider "how good" I feel that xFIP is the best measure which is the pitching 3 true outcome. In a 2017 comparison of SPs with 150 IP Cobb was 38th of 71 and Lynn 55th.
I also compared the same in whip; Cobb was 49th, Lynn 47th. ERA surprised me when Lynn was 17th and Cobb 25th. This suggested that either very good defense or a shut down bullpen bailed them out.
Both pitchers had DP frequency of 15% (11% MLB avg.) which was a pitcher getting a GB when needed and possibly a good defense as well.
Both had good LOB%; Lynn was 9th, Cobb 25th which minimized the effect of the shut down bullpen consideration, because the Cardinal BP allowed 61% of Lynn's inherited runners to score and the Rays allowed 37% of Cobb's runners to score.
My impression based on xFIP in which both Cobb and Lynn gave up HRs at a higher percentage than avg. Both had below avg. strikeout rates, and Lynn also had a higher BB % than avg., while Cobb was lower than avg. leading to a somewhat better xFIP position. Neither had exceptional defense behind them with both teams defenses in the lower half of their leagues.
I believe that both pitchers, flawed as they are, were able to help themselves to get out of frequent trouble based on whip, by getting the opportune DP or timely strikeout.
Middle of the rotation pitchers, probable improvements on Wheeler, Gsellman, Matz or Lugo might be if they could stay on the field. Not advocating going after them with too many uncertainties with the Mets.