The issue is that he had to play 19 minutes a game for an entire season to get that level of production, which isn't even that special in the first place. Girgensons had a 1.33 ES points/60 in 2013-2014 and a 1.49 ES points/60 in 2014-2015, which isn't even that good anyway. For comparison, Bonino in 2015-2016 was at 2.08 ES points/60 when he was MIA for the first 50 games of that season and was at 1.49 ES points/60 last season (he wasn't good at all at ES last year, but he still matched Girgensons' best).
If Girgensons matched his career best in ES points/60, he would match what Bonino did at ES last year (which was not good, I should reiterate), assuming you gave Girgensons the same minutes and zone starts that Bonino got. Take Bonino's production, take out his PP production and I think you'd have what Girgensons would do as a 3C here most likely: around 12 goals and 25 points. Oddly enough, that's almost exactly the same as what Sutter produced in 2013-2014. I don't think that's awful production, especially when he would be playing super heavy defensive minutes, but that's not exactly good 3C production. Maybe he could do more by playing more offensive wingers with him (maybe getting Kessel more defensive zone starts would actually help improve his production, because it allows him to streak down the ice and use his speed and shot), but I'm not sure if you want to put guys like Sheary or Guentzel in heavy defensive minutes