Rule

Conclusion: Heatran heavily relies on predicting switch-ins correctly to stand a chance against most of these Pokemon. In a one-on-one without switch-ins, Torterra is the only safe win (assuming Fire Blast hits), a win against Iron Treads depends on its set, and a win against Gastrodon is only possible if Heatran is run with HP [Grass]. The meme therefore checks out. Let me know if I missed anything because I haven't done any competitive stuff since Gen 5 :3

Jesse what the fuck are you talking about
- When you were partying, I studied Pokemon VGC recordings. When you were having premarital sex, I mastered the Gen 4 OU and Uber meta. While you wasted your days at the gym in pursuit of vanity, I cultivated Pokemon on an old Heartgold cartridge. And now that the world is on fire and Team Rocket is at the gate, you have the audacity to come to me for help.
I would add the minor point that I've also seen heatran running air balloon instead of life orb :)
- Right, Air Balloon was all the rage back in Gen 5 and I completely forgot about it! Thanks for pointing it out :3
  The reduced damage from it might turn some 2HKOs into 3HKOs, but as long as Heatran outspeeds the opponent (e.g. Hippowdon), that should be fine because they'll probably waste a turn figuring out it has a Balloon and then need another turn to pop it.
Hidden Power doesn't exist in Gen 9. Although you can use Tera Blast with the appropriate Tera type to replicate that. Note that using your Tera on Heatran will also change your defensive typing for the 3 turns (?) it lasts.
- It's good to know that Hidden Power doesn't exist in Gen 9, thank you :3
  Heatran would probably stand a slightly better chance against some of them with Tera types, I reckon. Tera Grass would give it a Ground resistance (Flying would make it immune, but then it'd be vulnerable to Rock-type moves and have no way to deal significant damage), and Grass-type Tera Blast would safely 2HKO Hippowdon, for example. Even a mono-Fire typing would allow it to survive Hippowdon's Earthquake and, with some luck, 2HKO with Fire Blast.

If only green could pay so little for such a big boy. I would love to have some turn two 8/8 creatures.

Easy peasy, just go turn one island + lotus petal, turn 2 Island crack petal for blue, cast show and tell putting Giant Ankheg into play. Boom 8/8 on turn two in your green deck!
- Dang, that seems like a pretty good combo. Too bad I'm running Green, Black, Red.