I'm a long-time player of Nautilus, and I play him almost exclusively as support. As he is right now, he doesn't need any buffs.
Sure, he might not be the best jungler out there, but that's an issue about the jungle itself, where champs with the best combos of sustain and clear speed tend to be favored over all.
In top lane, he will get beat by a duelist if he tries to go 1v1, but he doesn't need to. Nautilus is a hard tank, and one with strong cc capabilities. He doesn't need to "beat" the duelist in his lane, but rather just survive until the end of laning, when Nautilus starts to shine by working with his team.
As support, he's actually still pretty good. He definitely better than Blitz, by far, in terms of utility and enabling the ADC. Against AP ranged mage supports, he might struggle, but not as much as one would think. Nautilus does decent burst damage at low levels, due to his passive. With his W, he can win on trades in lane against squishier supports. If the Stoneborn Pact keystone Mastery is selected, Nautilus' passive can also provide some healing for his ADC.
Yes, the new tank item adjustments hurt Nautilus in terms of his W, but the loss in health is nominal. He still can bring up a big ass shield, and it's further bolstered by the slight increase in resistances. To say that Nautilus has poor scaling into late game outside of his cc, is to completely miss the point of the champion! Nautilus is all about his cc, which works just as well in the late game as in the early game. You don't play Nautilus for his damage potential, you play him to lock down the enemy and be a meatshield when his abilities are on cooldown.
Now if you want to throw in win rates, that's fine, but that just tells me there are many players out there who just don't know how to play Nautilus. Hell, I've seen Nautilus players prioritize AP on their builds, and they usually end up failing because his damage is still not impressive with a lot of AP and they get dropped fast because of the lack of defense.
There's no specific probablem stated, so I can't respond to what the OP perceives as "underperforming." If he can give better details, then maybe I can see what he's doing wrong.
