-Bad Stealth Rock setter because it can't keep them up at all vs common removal options (Tusk/Treads dominate it, Corv sits on it).
Tusk wants nothing to do with arch, as draco meteor absolutely smokes it. Treads doesn't like taking bp's on the switch.
252 SpA Archaludon Draco Meteor vs. 0 HP / 4 SpD Iron Treads: 138-162 (42.9 - 50.4%) -- 2% chance to 2HKO
0 SpA Archaludon Draco Meteor vs. 0 HP / 4 SpD Iron Treads: 113-133 (35.2 - 41.4%) -- guaranteed 3HKO
Plus, treads doesn't exactly relish switching into draco meteor.
-Dragon/Steel with strong physical bulk but mediocre special bulk, and its offensive prowess is pretty unspectacular without investment and no way to boost it. And if you don't invest in bulk, then it gets overwhelmed too easily.
AV alleviates that a decent amount, and honestly, you probably will be taking physical attacks. Tusk has poor special defense, and yet that doesn't really hold it back a lot. And due to its typing and stamina, it can take many hits if it doesn't invest, though ofc, not nearly as well.
-Does not wall DNite who literally EQs it (which kills at +1 with minor prior chip), Gliscor literally chips it down longterm with EQs/knocks its lefties off (and no, Mola is not a solution to this). Hamurott gets free spikes, Sacred Sword variants slice right through Arch.
D-nite and Gliscor, sure, but samu clicks ceaseless, and then has to deal with +1 arch who could potentially bp on it. Also sacred sword is only at 14% usage last month, it is an option, but not a common one.
-And then it clicks knock, removes your lefties and gets shredded by spikes.
Still a good offensive switchin.
+2 252 Atk Wellspring Mask Ogerpon-Wellspring Play Rough vs. 0 HP / 0 Def Archaludon: 177-209 (55.1 - 65.1%) -- guaranteed 2HKO
+2 252 Atk Wellspring Mask Tera Water Ogerpon-Wellspring-Tera Ivy Cudgel vs. 0 HP / 0 Def Archaludon: 197-232 (61.3 - 72.2%) -- guaranteed 2HKO
If it can take even +2 hits decently well without investment, just imagine with just hp.
+2 252 Atk Wellspring Mask Tera Water Ogerpon-Wellspring-Tera Ivy Cudgel vs. 252 HP / 0 Def Archaludon: 197-232 (51.3 - 60.4%) -- guaranteed 2HKO
+2 252 Atk Wellspring Mask Ogerpon-Wellspring Play Rough vs. 252 HP / 0 Def Archaludon: 177-209 (46 - 54.4%) -- 55.9% chance to 2HKO
Also the archaludon player would not just ideally let spikes go up for free. Something like tusk would try to spin them away, so yes, it can be good into wellspring. And frankly, making waterpon not run play rough as often is always a good thing, anything to limit that mon. Kyurem would do better against waterpon as +2 knock off doesn't OHKO it, while bolt feasts on it. Roaring moon can now switch into it a lot easier.
Its stab combo is walled by all our good steels (which we have no shortage of).
Yeah, that is a negative to it. Still threatens kingambit, tinkaton and treads with bp, so they aren't really switching in for free. Corv, ghold and others can switch in, but Arch teams will still have answers to them.
That Kingambit calc is super silly because assuming endgame? That Gambit will be realistically +2. And unless your also packing Tera still that late (unlikely), you lose.
+2 252+ Atk Black Glasses Kingambit Sucker Punch vs. 0 HP / 0 Def Archaludon: 247-292 (76.9 - 90.9%) -- guaranteed 2HKO
+2 252+ Atk Black Glasses Kingambit Sucker Punch vs. +1 0 HP / 0 Def Archaludon: 165-195 (51.4 - 60.7%) -- guaranteed 2HKO
Archaludon doesn't even need to invest in speed to outspeed kingambit, and it easily switches in on iron head in order to get that stamina boost.
0 Def Archaludon Body Press vs. 0 HP / 4 Def Kingambit: 248-292 (72.7 - 85.6%) -- guaranteed 2HKO
Now yes, it doesn't OHKO in return, but it heavily, heavily chunks it back. And honestly, kingambit won't want to stay in really.
+1 0 Def Archaludon Body Press vs. 0 HP / 4 Def Kingambit: 368-436 (107.9 - 127.8%) -- guaranteed OHKO
So yeah, archaludon is a decent answer into kingambit. It ofc wouldn't be the only mon you use for gambit, but its a nice stopgap.
It wouldn't be amazing at all. Seriously I feel like so many are theorymonning based off of on paper things without considering its flaws without EShot. Want a good steel rocker? Tinkaton does it while also compressing checks for tough-to-answer nuisances like Darkrai and Kyurem, and with fast Encore can trap slower set up threats to neutralize them sometimes. Want a defensive steel? Gholdengo and Corv pack recovery, the former being a huge offensive threat while the former has great momentum gaining utility, and Iron Crown is aggressive and disruptive to most teams. Offensive? Again, Gholdengo, but also of course Kingambit for obvious reasons as well as Scizor on offense, Iron Crown in general. Non rain Arch does not compress any useful roles together well, and it's unremarkable.
Okay, this isn't really theorymonning. When arch was in the meta, it was good outside of rain teams, as it provided ways to deal with powerful threats. Waterpon was running superpower, which was just for arch. Archaludon would be a great mon in the tier. Can gholdengo threaten kingambit without having to rely on bogus blast while still being a powerful offensive threat? Can corviknight potentially set up rocks while dealing with waterpon and making it switch out.
The reasoning why archaludon was broken on rain, was as you've said, are due to a multitude of factors that combine with e-shot. Just dismissing these positives I don't get. It could still be good on teams that need a temporary waterpon, kingambit switchin, while providing good damage and utility to a team. T-wave and dragon tail are options for it too.