Lugia isn't really the best wall this generation because it simply sits there and phaze. Unlike Giratina it does not block spin, which is crucial for almost any team. No team will want their hazards removed, and Lugia just invites them all, any Rapid Spinner can come in for free on Lugia unless you use surprise moves such as Weather Ball in the sun to KO Forretress or Hydro Pump in rain to smash Excadrill.
That said, Lugia has huge bulk and can sort of check Extremekiller, if Stealth Rock is up, Lugia will likely lose unless it gets a chance to use Roost. I think fast Lugia has a better chance this time thanks to Multiscale, and it beats Swords Dance Rayquaza better. If you are max Speed, you can wall any slower Latias or Latios thanks to Roost and non Scarf Terrakion will lose to you, especially when you are carrying Reflect. Bold Lugia loses to Sword Dance Rayquaza with V-Create if Stealth Rock is up, which is a pretty common situation.
Having mixed bulk is nice, but Lugia's role can be substituted by others who do more than walling, usually in the form of Arceus. For example, Fighting Arceus can hit things hard directly, epecially those dangerous to stall such as Excadrill and Dialga. Lugia simply lacks the offenses and utility of some other pokemon, and sheer bulk and phazing are the only things going for it.
No other wall can match Lugia's bulk, especially with Multiscale, and it is one of the few walls who can outstall Ho-Oh, as long as you use Reflect and Pressure. Immunity to Spikes is a bonus but you are forced to use Substitute to avoid status and Leech Seed.
I think Calm Mind Lugia is a pretty good set simply because it gives Lugia some sort of offense while phazing at the same time. Most Calm Mind users simply cannot overpower Lugia as you phaze them out, such as Mewtwo, Latias or some Kyogre without Thunder. Regardless of what Lugia uses, something will wall it hard so Whirlwind is a good move even on Calm Mind sets. Multiscale lets it grab the first boost even easier, but you must realize Lugia has lousy offenses and just Aeroblast as its powerful STAB. Psyshock is weak and things that stop Lugia usually laughs at it, such as Zekrom, Tyranitar, Excadrill and Forretress.
Kyurem-W wasn't fun for Lugia either, unless you are running Light Screen, once you are at 100%, you can no longer Roost on Ice Beam and Specs ones will OHKO you. Scarf 2hKOes Lugia regardless although Genesect is safely walled outside of boosted Thunders. Kyurem-B isn't a big threat because Lugia outruns it and can throw up a Reflect before it gets to attack. Latias isn't really threatening to Lugia but it can annoy it with Thunders.