The idea that Garen is a 'low elo pubstomper' is completely wrong.
I just had a game as Jhin where a low Platinum Garen basically dumpstered my entire team of Diamond players (and a Gold Lux). He ended the game with something like 4x more damage than the rest of his team. Making the implication that we just don't know how to play the game well is absurd.
Even with Leona, Lux, Elise, and I chaining our CC perfectly, it was still like fighting a raid boss, and he often still managed to either disengage before dying or connect with one or two of us, because we just couldn't outrun him. In this specific case, he had Yuumi attached to him 24/7, but a team that didn't have four forms of CC would have faired much worse.
This is insane, given that this player was literally doing nothing but running in a straight line for us and eating everything we threw at him. There was absolutely no skill component involved. I could throw down traps in front of him, and he would just barrel through them without bothering to sidestep.
His damage is way too high with the recent changes, given that he can now viably stack movement speed items and 100 to 0 any carry in 1-2 seconds if he makes contact. Which is incredibly hard to stop him from doing when he's breaking 600 movement speed and stacking so much tenacity that CC basically does nothing.