So then what is Gyarados used for? (Beside gym species clause) No quick water move?
Especially when all it used to have was Bite as a Quick move before Dragon Tail?
Even with good Attack Hydro Pump is outclassed by the 2nd Outrage hit which is outclassed by It's use on Dragonite. Stab isn't the most important especially now when Super Effective coverage is 1.4 and STAB is 1.2. You can check the article I mentioned a couple of posts back, also didn't we just cover Lugia with Hydro Pump?
Gyarados isn't particularly good for anything; as a Water-type, Vape outclasses. As a generalist, Dragonite outclasses. I'm aware STAB isn't primordial, but tell me, what is Gyarados gonna do with super effective coverage? If it has Dragon moves, it is (presumably) meant to counter Dragon-types, and guess what, Fairy-types (double resist to Dragon and access to Dazzling Gleam) and Ice-types (fast AND charge moves for double damage) do that better than Gyarados. I guess Gyarados with dual Dragon beats Kingdra better than Dragonite beats Kingdra??? Dark-coverage Gyarados hits... Psychic and Dark types... this is done better by a Dark-type by Tyranitar who not only gets STAB but resists their main moves. I guess Gyarados resists Focus Blast? lol
Gyarados's previous claim to fame was its CP; now, it's just outclassed. It's perfectly usable, but there are better Pokemon out there.
Lugia's case is different, because we are talking about defensive Lugia with Hydro Pump. Offensive Lugia should never use Hydro Pump, lest it wants to be an outclassed generalist / tank.
(Lugia with Hydro Pump, Gengar/Alakazam with Focus Blast, etc. are additional examples of how good coverage helps them better handle their own checks like Tyranitar, and they can still handle their original targets with the other move that gains STAB).
You can do this but they end up being completely inferior to other counters (in the case of Gengar and Alakazam, they do NOT want to face Tyranitar or anything even WITH Focus Blast because they are glass cannons lol). Attackers are much better refurbished to handle specific things they beat, not tailored to beat everything and do that sub-optimally. For example, a Psycho Cut / Focus Blast Alakazam now fares worse against Poison types by default just to be able to hit Tyranitar (if it is not dead by Crunch lol) and Blissey a little harder (too glassy to do this).
Gyarados countering Dragonite with Dragon moves is another example.
See above. A Fairy-type or Ice-type does this better than Gyarados can. Dual Dragon Gyarados I guess beats Dual Water Kingdra better than anything else?