I've been saying this for a long time. The key for Porcello is his HR/FB%. If he is around 9.5%, you will see a solid No. 2 pitcher in the rotation. If he can't keep the ball in the park and keeps posting those horrendous 14+% HR/FB% (which will be an up-hill battle in the ALE for him), he will suck again.
i.e. If his sinker doesn't sink, he will be in trouble. His fastball is a blank check. Only 30% of his pitches last year were sinkers, while in 2016 the percentage was 40, when he against odds won the Cy Young —although his BABIP/LOB% were the lowest/highest of his career (269/74). The lucky dragons taxed him in 2017.
IMHO and as I said before... the coaching staff can't do much to improve this guy since the talent simply isn't there.
Hopefully and at least the lucky dragons (BABIP/LOB) favor him again this year, like they did in 2016.