ERA was created to accommodate pitchers. Not only do runs caused by errors by the other players not count, but also runs caused by the pitcher's own errors. Indeed, if a pitcher (like ERod) simply doesn't bother to cover 1b on a grounder to the right, it's a single because pitchers shouldn't be required to contribute to the defense. ERA+ simply furthers the process of accommodating pitchers.
Nevertheless, I think ERA is the best measurement for pitchers over the long term. That said, I do agree with Kimmi and others who point that there is value in a pitcher who can be relied upon to pitch 5 or more innings every 5 days and to do that season after season after season.
In his 5 seasons with the Sox, Porcello started 28, 33, 33, 33, and 32 games. In 2018, the Sox best season ever, Porcello pitched more innings, 191.1, than Price (176) or Sale (158), had 16 quality starts to their 18 (Price) and 17 (Sale), and had the most wins, 17 (while losing 7). He even pitched 15.1 innings in the postseason with an ERA of 3.52. Only Price (26 innings, ERA 3.46) and Eovaldi (22.1 innings, ERA 1.61) were better.
I'm not a Porcello fan, but credit is due.