The argument I'd make is that the "depth" I think you need to contend would likely require acquiring someone good enough to actually be in that Crosby, Malkin and Letang group. I think that even prime Crosby, Malkin and Letang needed that. The Penguins obviously wouldn't have won either cup in 2016 or 2017 without Kessel. Now, you don't have Kessel and your core is worse.
You obviously have to criticize the support cast for this team, because this support cast wouldn't even be good enough if you took 2015 Crosby, Malkin and Letang and put them on the Penguins today. The next level question for that is whether Crosby, Malkin and Letang are good enough today to be the best, 2nd best and 3rd best player respectively of a cup caliber team. I'd say Crosby is, but I'm not confident in the other two.
That last question is whether the "do you need a new Phil Kessel?" comes in. At this point, I think you can legitimately argue the "support" you need for the Crosby, Malkin and Letang core is someone good enough to challenge Crosby for the primary member of that core.