Again, coming back to the two types of Salamences: Wall-breaker Mixmence and Sweeper D.D. Mence
First, starting with the wall breaker, Mixmence:
@Mixmence--
Wallbreaker: Job is to defeat 1 enemy pokemon.
Here's the problem though, Salamence is not the only pokemon designed to do this job, and looking at other pokemon meant to take out specific targets, it's got significant weaknesses compared to others.
Summary of the set and performance: Naive with Draco Meteor / Fire Blast / Earthquake / Outrage is without a doubt the most effective. I base my opinion on having used this set in 80% of my battles until now, and having used the exact same set with Stone Edge over Outrage pre-platinum. Generally speaking, Mixmence is not as good late game as many other sweepers-- imo. Flygon, Breloom, Lucario, Empoleon, Metagross-- pokemon with a natural resiliance to passive damage and/or a powerful setup sweep strategy are generally better late game. Mixmence's real time to shine is early-mid, where he is able to break defensive loops that would otherwise be very frustrating to beat.
While it is possible that Salamence will be able to take down multiple enemies (usually only likely to happen against slow teams late game), or have itself out-predicted and killed without accomplishing much about, those types of outcomes are relatively rare. Salamence will likely come in the early/mid game against a slower enemy either on a resisted switch or revenge kill, and likely see 1 of 2 likely outcomes.
The two most possible outcomes:
45% chance: Salamence makes 1 kill, but having been forced to use Draco Meteor or Outrage as well as accumulate LO, sand and SR damage, is left weakened both offensively and defensively to the point where it is easily revenged (if not immediately revenged due to being locked in Outrage), so that it will either die or be forced out to be used as little more than death fodder later on (with a slight chance of pulling off one more desperation attack later, but will likely not be given that chance).
45% chance: Salamence dies while having done around a total of 70~90% damage to one or more (ie. 2 pokes with 40% damage each) enemy pokemon.
As a pokemon designed to take out one enemy pokemon, here is the pros/cons:
Pros: Powerful STAB with broad neutral coverage and excellent attacking stats from both sides. This really is what makes Salamence tick as a wallbreaker-- the fact that unlike Infernape, its primary STAB is both widely unresisted and comes from much higher base offensive stats. The nice thing about Mixmence is that he has very good odds to put the hurt on something, and while he somewhat limited to achieving optimum performance early/mid game, he's got relatively good flexibility during that time frame and can come out and do his thing on a number of enemies (anything slow that will naturally be defeated 1 on 1 by mixmence).
Cons: Salamence takes out the enemy at the cost of its own life, AND it has no control over what it kills. Because of LO (which it needs), Sand (which it wants) and SR, Mixmence is falling to easy revenge kill via scarf, priority, or simply faster pokemon. While pokemon like Magnezone, Scarf/bandtar, Scizor all have the capacity to force the kill of certain pre-determined targets, Salamence is unable to stop the opponent from simply switching in Death Fodder while Salamence continues to fall to residual damage and the effects of its own attacks regardless. Compared to more defensively built pokemon as well, such as Skarmory, Rotom-A, Swampert or Vaporeon, who can switch in easily against specific targets and are almost guaranteed to make very good use of turns by achieving specific objectives, Salamence is severely lacking in consistency and dependability.
This is where SR comes in, really denying Salamence the second chance if it hits the wrong target on this step.
If Mixmence were a Yu-Gi-Oh card, it would read: "Sacrifice this monster to destroy one enemy monster, your opponent gets to choose which one."
This would be a really crappy card effect. The reason is a question of resources, simple economics: This is a 1-for-1, you are losing one pokemon (by dropping salamence into a much weaker state) to kill 1 enemy pokemon (or at least weaken some stuff), an even trade if not for the fact that the OPPONENT gets to choose, and can simply make Salamence' efforts in vain with death fodder or just smart switching.
The only reason why Mixmence is "good" economically, (not great, but good) is because in the event it makes the kill, even if severely weakaned it can serve as death fodder (and relatively good death fodder using intimidate), with a slight chance of getting to throw out an extra meteor/rage later on if it gets lucky.
Looking at the picture in a broader sense than sheer comparative resources (how many pokemon you use to make how many kills), Salamence's real strength is in setting pace. Mixmence is all about battle by attrition-- it forces a faster paced game with both sides taking losses (after all, it initiates a 1-for-1 trade). This can be seriously disruptive to teams that depend too much on teamwork to perform (aka. traditional stall and slower forms of bulky offense). In other words, when all of your pokemon rely too much on their teammates being around to perform, your team gets ass-raped by Mixmence because it forces a different pace to the game. Honestly speaking, I think it's a very good thing that there are pokemon who can break the circle jerk of resistance-based defensive switching. Pokemon is a team game, but one based on one-on-one battles-- and it is a BATTLE, it's a FIGHT, the game is and should be based on intelligent sacrifices and a war or attrition.
Offense, Bulky Offense, Semi-Stall, and Dedicated Setup sweep (Setup sweepers following in wake of Hazard/Screen/B-Pass users) are all teams built for and perform excellently in wars of attrition. Salamence's real strength means little to nothing to them in terms of setting pace as all have executable plans that take sacrifices into account (or rather their game plans accomidate for making certain sacrifices at certain points in a given game). In my opinion, this is a necessary skill for truly competitive pokemon-- losing pokemon is a part of the game. You have to build to be able to fight without your whole team, and have a plan that you can both execute and expect to execute regardless of when shit happens and you have to sacrifice. Of course the fact that mence is in the meta means it shapes the meta-- but then that can be said about ANY top 10 OU poke.
People rant about Salamence's power, but it's really easy to ignore the consistency and dependability lost by choosing to use a pokemon like Salamence. The reason why bulky offense (and stall at one poing) was popularized in the first place was due to strong consistency-- which is a huge benefit to playing that style.
If you are using hard-core wall breakers like Mixmence/Mixnape, you ought to know that you lose out on consistency to achieve power. Inversely, if you are choosing to ignore pokemon like Salamence/Infernape, you shouldn't bitch if you can't match it in power-- because you have already forsaken that power for higher consistency.
@DD Mence--
Mid-Late game sweeper: Job is to sweep, that is kill 3+ pokemon consecutively. If it does not kill at least 2, it does not perform its job (considering it is meant to get kills/end the game against weakened opponents).
Summary of Set Performance: Salamence comes in mid-late game when his counters/checks have been fairly weakened, and looks to sweep using +1ATK +1Speed and its powerful attacks.
Pros: Powerful STAB Outrage resisted only by steel backed by respectable Fire Blast and Earth Quake means it has power and excellent coverage when compared to other late-game set-up Sweepers like Luke, Empoleon or Agiligross. You have more power and flexibility than late-game cleaning choice users like Scizor or Flygon.
Cons: You're trying to late-game sweep with only 75% of your HP. That is a big problem. Especially when you're facing sand, possible LO damage, and have no resistance of any kind to priority. Aforementioned other popular set-up sweepers Luke, Empoleon and Metagross all resist Bullet Punch and Extreme Speed, the most common priority attacks, as well as resistance to Sand and Stealth Rock. That does a lot in aiding their sweeping, especially when considering all these pokemon should be aiming to sweep against weakened teams. Late-Game Choice users like Flygon and Scizor also have excellent resistance against passive damage, and thanks to choice items don't even need a turn of set up. Flygon also lacks thunder wave weakness. One can even compare DD mence to the also very powerful Kingdra, who lacks SR weak, resists Bullet Punch, and has flawless Dual STAB.
All in all, DD mence is certainly a good pokemon, but put along side his fellow late-game offensive pokemon, he certainly has his own issues to work out as well.