Judging by the highest level of any Pokemon in the team being 50, your gym leader is placed 8th. Meaning that, while your Pokemon aren't as strong as the Elite Four members, they should be tougher than the other Gym Leaders before them. Meaning that natures and moves should correspond to their roles in a battle. While they may not have the best Pokemon, they should have competent movesets and natures to compliment their roles.
I also need Abilities on all of these Pokemon (including ones I have looked over). These are difficult to judge if there are no Abilities for me to gauge them on. Also, the weaker the gym leader is, the more lenient the attacks you can add to them are (just as long as the levels, forms, and lesser attacks make sense).
Salamence
Level: 40
Gender: Male
Nature: Brave
Moves:
Dragon Breath
Fly
Scary Face
Zen Headbutt
A Brave nature means Salamence has higher Attack and sacrifices his Speed. Scary Face can offset this. However, I'd like to know the Abilities. Nobody has really put Abilities on their Pokemon and it is really confusing. But if Salamence is probably supposed to be a physical fighter from what I can see, why do they know Dragon Breath over a much stronger Dragon Rush, Dragon Claw, Breaking Swipe, or Outrage, or even Dragon Tail? Dragon Claw might do more damage than Dragon Breath if Salamence's strength lies in its physical attack than its special. Fly is fine, as it is the only good STAB attack it can learn that isn't as weak as Aerial Ace or Dual Wingbeat.
Salamence is weak to Ice, Rock, Dragon, and Fairy. Dragon Breath (or any physical Dragon-Type attack you replace it with) can stop Dragon-Type Pokemon, Fly doesn't get rid of any weaknesses, and neither does Zen Headbutt. I would recommend letting it know Brick Break instead of Zen Headbutt, which can also get rid of any screens the challenger may use (which might be used), and helps get rid of Ice- and Rock-Types. Steel Wing is also great, and I might recommend getting rid of Scary Face just to have something to use against Fairy-Types.
Pidgeot
Level: 45
Gender: Male
Nature: Brave
Moves: Sky Attack
Heat Wave
Razor Wind
Mirror Move
Again, another Brave natured bird, which is probably not a good idea. Pidgeot's speed is key to its usefulness and having a nature that can negatively affect it won't exactly be a good idea. I can't tell if you wanted it to be another Physical attacker due to the nature and the better Attack stat than Special Attack, but I assume you wanted them to be a mixture. But I feel like Pidgeot is not good enough with this moveset in the 8th gym. Razor Wind is a two-turn attack, the first turn being a charging turn. I wouldn't recommend any two-turn attacks that need the first turn to charge, and there are better Normal-Type attacks to use. Mirror Move is good, Heat Wave is a staple to get rid of Ice-Types, Rock-Types can be rid by Salamence or Gyarados, and Electric can be taken care of by another member of the team.
To replace Razor Wind, I would recommend Return (which is MUCH stronger and uses Pidgeot's better Attack stat). That's actually it. There are no other Normal-Type Special attacks that are a good idea on Pidgeot. I would also recommend making Pidgeot's nature be something else that doesn't impact Speed negatively. You never do this, but seeing that Speed, Special Attack, and Attack are needed, one of its defenses will have to be sacrificed, so it will have to be Defense for now. Lonely, Modest, or Timid would be good ideas.
Crobat
Level: 44
Gender: Male
Nature: Brave
Moves:
Air Cutter
Confuse Ray
Leech Life
Venoshock
Crobat is also a high Attack and Speed Pokemon, so Brave is not a good idea. I wouldn't even recommend its Special Attack stat. But let's have at it with both sets.
First Crobat is weak to Rock, Electric, Psychic, and Ice. Ice and Rock can be taken care of by Salamence, and Electric and Psychic by Pinsir. So Crobat is basically fine.
For a physical set, Leech Life is a given for much-needed health, Cross Poison as the strongest Poison-Type physical attack it can use, Sky Attack/Brave Bird/Fly for strong Flying-Type physical attacks, and Crunch to help get rid of Psychic-Types. Though, Crunch isn't the most ideal move, and Defog might be better to help get rid of screens and hazards (which are very annoying).
For a special set, Giga Drain is a given for health, Air Slash or Hurricane for strong Flying-Type special attacks, Sludge Bomb for a strong Poison-Type attack and a 30% chance to poison, which can either make its last move Hex (which doubles its damage if the opponent is poisoned), Dark Pulse, or Defog.
Pinsir
Level: 50
Nature: Brave
Moves:
Bug Bite
Storm Throw
Double Hit
Vise Grip
I assume Pinsir has a Pinsirite to become a Bug/Flying-Type Mega Pinsir with Aerilate. Pinsir is much better as a physical attacker and it needs its speed, so Brave needs to be changed for Adamant. Flying, Rock, and Fire (and then after Mega Evolving, Electric and Ice) are its weaknesses. Rock Slide, Rock Tomb, or Stone Edge are much better options than Double Hit, allowing it to knock out Flying, Fire, and Ice Pokemon with ease. Earthquake is also much needed to get rid of Rock, Fire, and Electric Pokemon, making it a beast and that can be replaced for Vise Grip. A Bug-Type attack can be X-Scissor, which is much better for an 8th gym leader. Instead of Storm Throw, which forces the Pokemon to go last, I would suggest either Body Slam, a strong Normal-Type attack that can become Flying and has a chance to Paralyze, or Feint to smash through Protect and Detect. Or even Thrash, or Double-Edge, or even Giga Impact if you feel inclined to go that route.
Gyarados
Level: 44
Gender: Male
Nature: Brave
Moves:
Splash
Whirlpool
Twister
Ice Fang
Gyarados is a better Physical attacker than Special attacker, so Brave or Adamant is better. Rock and Electric can be practically destroyed by Pinsir's Earthquake, but letting Gyarados have Earthquake is much better. Aqua Tail is the strongest Water-Type attack it can use, and Bounce is the strongest Flying-Type attack it can use. Unless you are planning on using Normalium-Z for Splash and get an added +3 in Attack, I would recommend Power Whip to get rid of Rock, Ground, and other Water-Types.
The problem with that is this entire team is a physically hyper offensive team. There are no walls, no Special Attackers, and no set-ups. With the composition of this team, I don't think this can be an 8th gym leader. Maybe 7th. You'll need Pokemon like Mandibuzz (or any other tanky Flying-Type) as a wall and Sigilyph (or any other powerful special attacking Flying-Type) to be a Special Attacker in order to be considered for an 8th position. That will literally be it though. And those are just my thoughts. If MrNinja says otherwise, then I guess it's fine, but a better made Gym Leader before this one can beat this one with ease.