I think Graves was horrendous in the pre-season but I think people exaggerate how truly bad he was. At 5v5 last year, he finished with a 1.98 GA/60, he really wasn't getting scored on. The issue is that he also wasn't on the ice when they were scoring either, he only had a 2.03 GF/60. His GF/GA and xGF/xGA results were very similar to Eller's last year.
He's a low impact player that you doesn't move the needle when playing well and makes some atrociously awful bad plays now and then. He's a $2.5 million #5 D that's overpaid by nearly 2x in money and by 3 years. If he was on a 3 year, $2.5 million AAV deal, I think the complaints about him would be quieter. Not gone, but quieter.
Graves is a defenseman version of Acciari that's making comically more than he's worth.