Darkrai is perfect where it is and a wall of irrelevant calcs doesn't change that. Nobody runs Modest Darkrai, 104 HP Xern, -SpD Mega Mence, or 128 HP P Don. Focus Sash is also generally a poor item for Darkrai to hold. With that said, Darkrai's viability is slightly hampered by the fact that it can only really fit on offensive teams, is in competition with Yveltal to an extent, and is susceptible to revenge killing. It's not the kind of thing that automatically contributes to any team, and it doesn't even always fit on every offensive team. Defensive checks may be tricky for it because of how unique Darkrai is as an offensive threat, but any good team can handle it once something is used as sleep fodder (several teams also run a dedicated sleep absorber intended to counter Darkrai).
Lugia is the polar opposite which for obvious reasons is dead weight for any offensive team. While it has immense bulk, this is often circumvented through Stealth Rock, Taunt, and status; there are even some offensive mons that can outright OHKO it. It's a good defensive Poke, but A+ is far too generous imo, especially when several of the threats you intend to check with it can break you under certain conditions (Mega Salamence and Primal Groudon). It is also very passive which I don't consider to be a very good thing, especially when you look at Pokemon in A+ that can be used defensively but still posses some offensive presence or ability to stallbreak. I don't consider Lugia to be a Pokemon that requires minimal support to be used, nor do I find myself always going to it as my first choice for the roles it accomplishes, both of which are part of A rank criterion.
Lugia is the polar opposite which for obvious reasons is dead weight for any offensive team. While it has immense bulk, this is often circumvented through Stealth Rock, Taunt, and status; there are even some offensive mons that can outright OHKO it. It's a good defensive Poke, but A+ is far too generous imo, especially when several of the threats you intend to check with it can break you under certain conditions (Mega Salamence and Primal Groudon). It is also very passive which I don't consider to be a very good thing, especially when you look at Pokemon in A+ that can be used defensively but still posses some offensive presence or ability to stallbreak. I don't consider Lugia to be a Pokemon that requires minimal support to be used, nor do I find myself always going to it as my first choice for the roles it accomplishes, both of which are part of A rank criterion.