Human Garou in the Webcomic might scale to Mirror, who's Town level.
Suiko was only powerful enough to become an A-Class Hero.
By the time of the Garou fight, Suiryu had never activated his battle suit, so he easily killed a Demon level threat with just his normal abilities. This means Suiryu is stronger than Suiko and capable of becoming an S-Class.
Suiko used her strongest move, which is explicitly designed to increase attack power, to put a scratch on Mirror (he explicitly says 0.4% damage, so it's not a paint scratch, it's actual damage). Suiryu has this exact same technique.
After activating the battle suit and then releasing his limiter to boost his strength massively, Suiryu described the battle suit's power as so much more potent than his martial arts abilities that it damaged his ego. Yet, Garou withstood every single one of these blows with a light nose bleed.
Post-Monster Garou is back to his previous level of strength, with even Bang being able to severely injure him without using much effort.