I really like this team, and it has a very similar build to one of my professional teams. Changes will be in bold.
Politoed @ Sitrus Berry
Ability: Drizzle
Nature: Bold
EVs: 252 HP / 140 Def / 76 SpA / 36 SpD / 4 Speed
Scald
Icy Wind
Helping Hand
Protect
Perfect. This is the exact set I use on Politoed.
Swampert @ Swampertite
Ability: Damp --> Swift Swim
Nature: Adamant
EVs: 108 HP / 252 Att / 148 Speed
Waterfall
Earthquake
Ice Punch
Protect
Also really good, use Damp to protect you from that very rare explosions, everything else looks good.
Rotom-Heat @ Safety Goggles
Ability: Levitate
Nature: Calm
EVs: 252 HP / 108 Def / 28 SAtk / 116 SDef / 4 Spd
Overheat
Thunderbolt
Will-o-wisp
Protect
You have a relatively frail team and really need some bulk, so at the expense of some offensive pressure, You became alot more bulky, which allows this Rotom to act much more as a pivot, which your team needs.
Gardevoir @ Choice Scarf
Ability: Telepathy
Nature: Timid
EVs: 12 HP/ 252 SpA/ 244 Spe
Moonblast
Psyshock
Shadow Ball
Hidden Power Ground
At first I changed this to Specs Sylveon. However I later realized you could make great use of Gardevoir Telepathy ability. So I am going to keep this relatively the same, but changed it to Psyshock so you aren't walled by certain Pokemon.
Bisharp @ Life Orb
Ability: Defiant
Nature: Adamant
EVs: 4 HP / 252 Att / 252 Speed
Sucker Punch
Knock Off
Iron Head
Protect
To start with Bisharp mingles well with your team better than Aegislash. I think the life orb variant of Bisharp has more to offer your team, even more so considering you have run protect anyway, but it is more personal preference.
Now we reach a small speed bump. You have Safety Googles on your team so Virizion losses some of its appeal. Really Stone Edge is a bad move, it can make close games blowouts with a single miss. So far looking in your team preview everything is predictable, Swift Swim Mega Swampert, you want something to keep them on the edge of their chair, guessing who your Mega is or what your lead is. You struggle against Ludicolo and Mega-Venusaur. I'm going to show you a custom build that I've worked on for a proto-type world's team of mine, but I move on and I haven't released it yet, so please don't post this on any other websites. However you have a good enough team, that I would be honored if you decided to use it!
Salamence @ Salamencite
Ability: Intimidate --> Aerilate
Nature: Adamant
EVs:116 HP/ 180 Att/ 72 Def/ 40 SpD/ 100 Spe
Dragon Dance
Earthquake
Double Edge
Protect
This is a bulky D-Dance Mega Salamence set. To start with the speed EVs are there to out speed neutral natured max speed base 100s, such as Modest Charizard Y. More importantly though there are many EVs invested in bulk, some examples that it is meant to take are a little farther down. 180 Attack and Adamant hurts, but its hurts even more at +1. At +1 speed he out speeds the entire Metagame evens threats that are positive natured 150 base speed. Use wisely that is the key. You have to predict switches or Protects in order to get that Dragon Dance off. Also your team could use the Intimidate from his base form. Furthermore it keeps your opponent guessing in the preview, because if they see Politoed they will assume Mega Swampert, and sometimes the better call will be to use Swampert, but you can catch them off guard with Salamence. You can catch them off guard a 2nd time, when the Salamence does not faint to an attack that it would be expected to. He is a hard core counter to the likes of Mega-Vensaur and Ludicolo. Double-Edge is main Attack, but can also make great use of Earthquake, keep in mind that you want him out there with Rotom-H or Gardevoir so that his ally is not damaged, but you could always protect for one turn with your other Pokemon considering Gardevoir is the only choiced Pokemon on the team.
EV set:
Offensive:
180+ Atk Mega Salamence Earthquake vs. 0 HP / 4 Def Mega Gengar: 154-182 (114 - 134.8%) -- guaranteed OHKO
+1 180+ Atk Aerilate Mega Salamence Double-Edge vs. 4 HP / 0 Def Mega Kangaskhan: 226-267 (124.8 - 147.5%) -- guaranteed OHKO
180+ Atk Aerilate Mega Salamence Double-Edge vs. 252 HP / 180 Def Amoonguss: 320-380 (144.7 - 171.9%) -- guaranteed OHKO
+1 180+ Atk Mega Salamence Earthquake vs. 4 HP / 0 Def Mega Manectric: 174-206 (119.1 - 141%) -- guaranteed OHKO
180+ Atk Aerilate Mega Salamence Double-Edge vs. 252 HP / 252+ Def Mega Venusaur: 188-224 (100.5 - 119.7%) -- guaranteed OHKO
180+ Atk Mega Salamence Earthquake vs. 0 HP / 0 Def Mega Lucario: 144-170 (99.3 - 117.2%) -- 93.8% chance to OHKO
180+ Atk Mega Salamence Earthquake vs. 4 HP / 0 Def Mega Tyranitar: 92-110 (52.2 - 62.5%) -- guaranteed 2HKO
180+ Atk Mega Salamence Earthquake vs. 252 HP / 0 Def Aegislash-Shield: 92-110 (55 - 65.8%) -- guaranteed 2HKO after Leftovers recovery
180+ Atk Aerilate Mega Salamence Double-Edge vs. 40 HP / 72 Def Politoed: 174-205 (102.3 - 120.5%) -- guaranteed OHKO
180+ Atk Aerilate Mega Salamence Double-Edge vs. 4 HP / 0 Def Charizard: 186-219 (120.7 - 142.2%) -- guaranteed OHKO
180+ Atk Mega Salamence Earthquake vs. 252 HP / 0 Def Mega Mawile: 80-96 (50.9 - 61.1%) -- guaranteed 2HKO
-1 180+ Atk Aerilate Mega Salamence Double-Edge vs. 252 HP / 0 Def Landorus-T: 109-130 (55.6 - 66.3%) -- guaranteed 2HKO
180+ Atk Aerilate Mega Salamence Double-Edge vs. 252 HP / 0 Def Sylveon: 213-252 (105.4 - 124.7%) -- guaranteed OHKO
Defensive:
252+ SpA Thundurus Hidden Power Ice vs. 116 HP / 40 SpD Mega Salamence: 156-184 (84.3 - 99.4%) -- guaranteed 2HKO
160 SpA Politoed Ice Beam vs. 116 HP / 40 SpD Mega Salamence: 156-184 (84.3 - 99.4%) -- guaranteed 2HKO
68 SpA Ludicolo Ice Beam vs. 116 HP / 40 SpD Mega Salamence: 140-168 (75.6 - 90.8%) -- guaranteed 2HKO
252 Atk Parental Bond Mega Kangaskhan Double-Edge vs. 116 HP / 72 Def Mega Salamence: 114-135 (61.6 - 72.9%) -- guaranteed 2HKO
252+ Atk Landorus-T Rock Slide vs. 116 HP / 72 Def Mega Salamence: 56-68 (30.2 - 36.7%) -- 51.2% chance to 3HKO
+1 252 Atk Mega Tyranitar Rock Slide vs. 116 HP / 72 Def Mega Salamence: 132-156 (71.3 - 84.3%) -- guaranteed 2HKO after sandstorm damage
252 Atk Tyranitar Stone Edge vs. 116 HP / 72 Def Mega Salamence: 134-158 (72.4 - 85.4%) -- guaranteed 2HKO after sandstorm damage
252 SpA Mega Salamence Dragon Pulse vs. 116 HP / 40 SpD Mega Salamence: 144-170 (77.8 - 91.8%) -- guaranteed 2HKO
252 SpA Aerilate Mega Salamence Hyper Voice vs. 116 HP / 40 SpD Mega Salamence: 73-87 (39.4 - 47%) -- guaranteed 3HKO
-1 252+ Atk Huge Power Mega Mawile Play Rough vs. 116 HP / 72 Def Mega Salamence: 146-174 (78.9 - 94%) -- guaranteed 2HKO
252+ SpA Pixilate Sylveon Hyper Voice vs. 116 HP / 40 SpD Mega Salamence: 152-182 (82.1 - 98.3%) -- guaranteed 2HKO
252 SpA Mega Manectric Hidden Power Ice vs. 116 HP / 40 SpD Mega Salamence: 148-176 (80 - 95.1%) -- guaranteed 2HKO
-1 252 Atk Parental Bond Mega Kangaskhan Double-Edge vs. 116 HP / 72 Def Mega Salamence: 76-91 (41 - 49.1%) -- guaranteed 3HKO
I hope that proves the effectiveness of this Salamence there are many more Calcs of things like Fake Out + Common Attacks but I can't recall them right now. haha!
Well I hope you liked the changes to the team that I made. But seriously though you built a very solid VGC team, keep up the great work. Enjoy the short amount of summer left!
-Unstoppable