This is why manual removal is the best form of nutrient export, and why it's the most effective method of accelerating the burnout of the algae.
Algae is a natural and necessary part of the ecosystem that most of us strive to recreate and maintain. It exists everywhere on natural reefs, and without it, the reefs would perish. Our goal is, or should be, to have it remain at a level that is visually acceptable and not harming or inhibiting our other desirable reef inhabitants.
Dumping drugs into the water might show positive visual effects, but to say that there were no side effects is probably untrue, and at the very least, misleading. Maybe you didn't notice side effects. Others have certainly reported undesirable effects, so maybe you were just fortunate. In all honestly, most of these kinds of treatments are akin to cancer chemotherapy, and should not be taken lightly.
I also have not the slightest bit of visible pest algae in my tanks, and have not for many years, despite having truly awful infestations in the early years and despite never having used any form of chemical or antibiotic treatments. So what seems to be a blanket statement that "no amount of water changes, or manual removal, or carbon dosing, refugium, or GFO, or clean up crew, or under feeding has ever done anything for my GHA" might apply universally is potentially quite misleading.
In any case, I greatly empathize with those battling algae infestations. It is a true test of patience. But it is a winnable battle, and without resorting to any extraordinary or unnatural efforts.