Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
I have changed some sections or added to the ones that you've suggested changes for, but I still am debating whether or not to remove the Life Orb set and have a Substitute one instead, so I'll try to get back to you on it.
I will admit that Hydreigon is a good user of Substitute because of the switches it can force, but the main reason I excluded Pokemon that can counter it but are weak to Hydreigon's coverage was because they were also slower then Hydreigon, meaning that they usually will not get a hit off before...
I mainly used a Life Orb, Choice Specs and Choice Scarf Hydreigon while testing out different sets, since I was under the assumption that Hydreigon's low speed would cause it to usually take damage before it can Substitute and cause it to only be able to use Substitute once or twice before...
[OVERVIEW]
Hydreigon is a very strong special attacker that can deal massive damage to many common Pokemon in the tier with the help of Life Orb or Choice Specs, and its offensive typing is also very good, being only resisted by Steel types, and it can learn moves such as Fire Blast to deal...