McGowan can be a high leverage reliever, a very valuable commodity..... and not exactly replaceable. I am sure McGowan can be an effective starter, the problem is at some point he will have a dominating game and be left in too long and BOOM
In 2008 McGowan threw a 125 pitch, 9 inning 4 hitter gem. Pitched 6 more games after that, averaging less than 5 innings, over 100 pitches just once... and was not seen in MLB again until 2011.
In 2010, Morrow threw a 140 pitch, 9 inning 1 hitter gem, one of the best games ever pitched, started 3 more games and shut down for the year. IMO he has not been the same pitcher since, loss of velocity and movement.
Both of these guys should be on a very strict pitch count. But of course, if they are dealing they will be left in and will be either gone for the year or history shortly after.