For some perspective....
Guentzel's career regular season points per game (0.94) puts him just a hair behind Barkov, Eichel and Point, but slightly ahead of Aho, Marchand, Tavares and Backstrom. For career playoff points per game his 0.97 is just behind Malkin and Point, just ahead of Pastrnak, Kane, Aho and Ovechkin.
Pretty much a point per game player across his career, including playoffs. His production peers are all 8-10M+ players, I don't see why 9M is a stretch here at all. He's about to turn 30, so the deal won't cross much into that ugly 35+ territory. I see no problem with this