Well here's my ERA & Run Prevention Estimator (RPE) Scale which apply to ERA, FIP, xFIP, SIERA, etc.
Under 3 Excelent to Elite —No. 1
Between 3.5 and 3 Very Good —No 2.
Between 3.5 and 4 Good — No 3.
Between 4 and 4.5 Mediocre/Average —No 4.
Above 4.5 Below Average/ Bum —No. 5
Said that, this is Porcello based on RPE:
ERA 4.40 (No 4)
FIP 4.06 (No 4)
xFIP 4.04 (No 4)
SIERA 4.1 (No 4)
He is consistently a No. 4 pitcher based on RPE; i.e. Mediocre/Average.
Based on fWAR he has a 29.6 fWAR through 11.4 years of service, i.e. 2.6 fWAR/year.
A 2.6 fWAR puts your pedigree as a SP in the 5th level out of 7 levels in the fangraphs' rule-of-thumb chart; i.e As Solid Player.
A Solid Player is not Good and way far to Very Good which IMO those levels are among AllStar, Superstar and MVP. It could be translated as Average/Mediocre.
MVP 6+
Superstar 5-6 fWAR
Allstar 4-5 fWAR
Good Player 3-4 fWAR
Solid Player 2-3 fWAR
Role Player 1-2 fWAR
Scrub Player 0-1 fWAR
As I said, Rick Porcello was/is not a Good pitcher by any means and way, way far to Very Good.