Its advantage is very small while Garchomp's advantage of doubling as a souped-up Dragonite and Rhyperior in one for Gyms and Raids makes it overall much more worth
If you dont have the legacy moveset, its only use is making people take three seconds to switch to Mamoswine on gym offense
If you do, its a good Dragon-Type in PvP
So... Yes, they are not equivalent
Aaaand... Chomp has better bulk, so it would do just as well in your raid scenario
Lets see, Dragonite can take on Palkia with Water moves better, and has more resistances - so bulk is relative to its type and not just raw stats (I.e. Steel types with less than ideal defenses can be better defensively and with TDO than others with better HP and/or Defense that take more neutral hits - especially after the recent Type-effectiveness changes).
In your post you said the opponent can just switch to Mamoswine if I use a Defender Dragonite, which actually brings up a great point, both relative to my recent point on Type-Effectiveness above and being “outclassed”. Can’t Mamoswine do a better job against most Dragons than Garchomp?
Ice can hit Dragonite, Salamence, Rayquaza, and even opposing Garchomp much harder than Garchomp itself, while also doubling down as a Ground Attacker, without a weakness to Dragon moves (making it harder for Garchomp to even stay in long enough even if it also dealt 4x effectiveness).
Same goes for Zapdos, and others like Dialga- whose Dragon moves deal more damage than its Steel moves.
Has Mamoswine already surpassed Garchomp before it even debuted? Yes when facing most dual-typed Dragons, and while Garchomp will be outdone by Precipice Blades Groudon, we know as of now that Kyurem cannot surpass Mamoswine because it lacks a currently available Fast-Ice Move.
Mamoswine is Future proof, Garchomp is not. And since Precipice Blades is already in the game master file as the best Ground move (Earth Power included), I think it’s Ground days are numbered - especially as Groudon also has higher bulk for TDO and DPS.
Ice is a better offensive type than Dragon, so while Garchomp may have stronger Ground moves, Mamoswine will overall surpass it in many matchups against Dragons.
Regardless, Dragonite can take Latios with Solar Beam, and other specific movesets better like Water Move Palkia. And as I mentioned for my Dragonite Raid, Rayquaza is unable to take as many hits and that means it doesn’t strictly outclass Dragonite (I.e. Fast Dragon moves still take a chunk out of Rayquaza).
So is Dragonite better than Garchomp - Yes in specific match-ups, yes in terms of Dragon move options (Dragon Breathe, Draco Meteor, Dragon Claw), and yes in terms of direct availability.
And no, Dragonite will still do better in raids if it has a Dual Dragon moveset such as Dragon Claw and Outrage to score additional hits, where it could have enough energy for Dragon Claw while Garchomp wouldn’t have enough for Outrage before fainting, or Dragon Breathe for more fast Damage and energy. Let’s focus on 2 Charge moves since you said Garchomp can be a Rhyperior and Dragonite in one. Without a second Dragon move, it cannot secure hits as much as Dragonite, as Garchomp has only Ground moves as another STAB option, which we all know doesn’t hurt Flying types much - like Dragonite in the raid I mentioned.
Garchomp will be better for when Megas are released and depending on future moveset changes.
Legacy moves on my Dragonites make them quite optimal for a variety of situations.
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For PvP these will fluctuate more, but it largely depends on what you are facing since unlike Raids and Gyms, you don’t know what your opponent has, plus for breaking Shields Dragon Claw is much more helpful than Outrage. Only Latios has better Attack with Dragon Claw.
