The way I see it, Porcello allowed 4-5 runs per game but could go 6-7 innings through that frame. Is it good? no. Is it a disaster? no —specially if you have a good offense behind.
That is just mediocre. That is what Porcello was in most part of his career.
Yeah, his durability is out of the question, but his quality is.
Thing is most of the times if you allow 4-5 runs you won't be pulled out. That's what happened with Porcello.