[Pocket]

Too big for me to check in one sitting - gonna offer feedback in piece meals ;x

Overview:
I am surprised you introduced Heatran without mentioning at all about its unique typing. Fire / Steel combined with its ability is the main reason why Heatran is the top OU Pokemon in BW2 despite the prevalence of Rain. Heatran possesses the offensive prowess of a Fire type coupled with the defensive prowess of a Steel type, resulting in this tanky nuke. In a way, the typing is a double-edged sword in a way, making Heatran extremely weak to common moves like EQ, Close Combat, and Surf, while giving it plethora of useful resistances, most notably resistance to Bullet Punch and Draco Meteors. While its typing turns Heatran into one of the best checks to Sun Offense, it's typing makes it one of the easiest preys for Dugtrio to eliminate. Its ability Flash Fire complete's Heatran's defensive and offensive build, by being immune to Fire moves, while boosting its own powerful Fire move further!

Offensive:

Peharps this makes Earth Power more important than even Heatran's STAB Fire Blast, as otherwise, other Heatran would be able to switch in with absolute impunity.

Nah, cut out the hyperbole - Heatran's powerful STAB Fire Blast to roast Ferrothorn, etc is more important than Earth Power's ability to eliminate opposing Heatran. Rephrase this

Heatran is able to defeat any Dragon-type that lacks a Fighting-type or Water-type attack.

What about EQ?

Will-O-Wisp can cripple any Fighting-type not named Conkeldurr, that would dare switching in.

Fighting-types don't usually switch into Heatran, so this is a weird sentence. Common targets of Will-O-Wisp would be common Heatran switch-ins like Tyranitar, Gyarados, Dragonite, and Terrakion. Rephrase

It also lets Heatran beat Dugtrio (especially useful if it use Life Orb), as Heatran can hit Dugtrio on the switch, and outspeed thanks to the Speed boost, and OHKO Dugtrio with Hidden Power or Fire Blast.

Another weird phrase in red - Heatran does not need Life Orb to beat Dugtrio. Maybe rephrase that LO is a particularly useful item for sweeping with Flame Charge in a separate sentence from Dugtrio.

never take out any EVs from this, as (especially if you don't use Life Orb) Heatran is otherwise too weak to fight back.

Again, cut out the hyperbole. Heatran will never be "too weak." Find a more precise way to describe your point.

4 SpD seems trivial at first, but prevent the rare yet very annoying Porygon2 from gaining a Special Attack boost. Although Heatran can still not do much back (unless it has Taunt or Toxic), it can prevent its teammates from taking too much damage from Porygon2's attacks.

Too much space just to justify 4 SpD EVs. Truncate this into a simple sentence, or even leave it entirely out, since it's largely irrelevant.

However, a bulky EV spread of 244 HP / 252 SpA / 12 Spe and a Modest nature is very viable, as apart from the aforementioned threats, there aren't much situations where Heatran will be in need of speed, and the extra bulk is very appreciated.

It's worth mentioning that with max HP, Heatran may run Chople Berry to comfortably survive hits from Terrakion, Breloom, and other fighting moves.

~ Good teammate suggestions

Specially Defensive:

~ Too much slashitis; keep it simple for the readers. That said, Taunt is a really useful move on defensive mons to prevent set up. I'll only ask to remove HP Ice and drop it into AC

It is a much more reliable way to spread burns, and can affect Poison- and Steel-types.

Remove phrase in strike out