The show built Homelander up as the ultimate threat. Someone who the Boys couldn't kill pretty much no matter what. Someone who every single Supe in the world was terrified of, because he'd kill them all easily. Someone who'd require months to even years of planning to develop any sort of method, which eventually cultivated in them needing to create a virus so strong it would wipe out every other Supe, possibly even all humans on the planet.
We know throughout the series that even Supes like Victoria Nuemann, who can literally blow apart your body from the inside out, likely has zero chance at doing anything to Homelander.
So yes, when a random guy with poison breath comes in and incapacitates THAT guy, who was once this seemingly insurmountable threat that the series spent its entire run building up as that insurmountable threat, I am going to look at that and question the writer's decision making.
It completely devalues all the previous efforts that went into making Homelander seem so intimidating.
Its like, if this guy could do that to Homelander, then why didn't we just get this guy in season 3, pull up with Soldier Boy, and end the show right there? Surely that'd be a lot easier than trying to make a world ending virus.
It has nothing to do with powerscaling or needing him to resist everything. If you paid attention to the writing of the show you'd understand why something like this comes off so poorly.