Hmm, this team is quite well structured, I will suggest some changes to help you overcome some of the problems you find with this team.
Onto the rate!
Looking at your current team, I see 4 Steel types that add to a huge Fire weakness, a huge Fighting weakness and a moderate ground weakness (You can abuse it to send in Air Balloon Excadrill to setup safely though). The first Pokemon that I would suggest replacing is Magnezone. Lets see:
-You need a special wall to put Stealth Rock on your Tyranitar.
-Skarmory(and possibly Ferrothorn) gives you problems.
To counteract these problems and to mitigate your Fire weakness, I would consider replacing Magnezone with Specially Defensive Heatran. This Pokemon brings with it:
-A Fire (and Will'O'Wisp) immunity, courtesy of Flash Fire
-A Special Wall that brings Pokemon like Volcarona to a stop due to its unique resistances, opening up more options for Tyranitar
-With Taunt, it provides an answer to opposing walls and setup sweepers
-Spreads burns with Lava Plume
-Smacks opposing Heatran without Air Balloon with Earth Power
Here's a set:
Heatran (M) @ Leftovers
Ability: Flash Fire
EVs: 248 HP/192 SpDef/68 Spe
Calm Nature
-Lava Plume
-Earth Power
-Taunt
-Toxic
With this I would change Tyranitar's set to a Support Smooth Rock set to prolong the number of Sand turns to 8 turns, giving Excadrill more turns to destroy teams.
Tyranitar (F) @ Smooth Rock
Ability: Sand Stream
EVs: 248 HP/252 Def/8 SpDef
Relaxed Nature
-Stealth Rock
-Ice Beam/ Fire Blast
-Crunch
-Stone Edge/Earthquake
With Ice Beam, it can act as a nasty surprise to opposing Landorus-T and Gliscor who otherwise pose problems to most of this team, or you can run Fire Blast to fry unsuspecting Scizor, Ferrothorn and Skarmory. Lure Tyranitar is quite uncommon and most people will expect Tyranitar to switch out, so it can nab surprise OHKOs that can give you an edge early in the battle.
As for Gliscor, I would run this set, it is pure evil:
Gliscor @ Toxic Orb
Ability: Poison Heal
EVs: 252 HP/4 Atk/252 Def
-Earthquake
-Toxic
-Protect
-Substitute
Once problematic Steels and Poison types are down, this Gliscor set wall a lot of physically inclined threats while stalling until the opponent dies of Toxic damage. Just use Substitute + Protect with no net HP loss due to Poison Heal and wait for the enemy to die.
Threat List
Just... No safe switch ins. Outspeeding your entire team outside of Excadrill in Sand, it can deal a huge amount of damage with High Jump Kick/Return/Ice Punch. Keep Metagross healthy to tank a hit if absolutely necessary and hammer it with a Meteor Mash/Zen Headbutt (Pray that you don't miss). Or whittle it down with Sand/Entry Hazards damage and revenge with Sand Rush Exca or Scizor, most likely sacking a mon in the process.
Specs variants are a nightmare to face for this team. Nothing can switch into it (No water immunity/resistance on this team) and you will most likely lose a mon while trying to bring Metagross in safely, where it can easily switch out and continue its rampage later. Play very carefully around it.
Can't really setup easily against this team, but if it gets a free DD off and Scizor is weakened, your team is in huge trouble.
I might suggest to change Scizor to Choice Band Azumarill to provide an answer for Keldeo, but I'm not sure if it will open up even more holes in this team.
