To get into a bit more detail :
The Heavy attacks have the Heavy Linesman property, which means armour sliding.
Using Opportunist as property makes it very easy to stagger Stormvermin packs.
The GS has a longer range than what you think. It outranges berzerkers and monks for example, so you can safely light attack them while kiting back. FK can stagger them quite easily too.
Merc is just a ratmower with it : if the horde doesn’t have armour, you can spam light attacks and absolutely obliterate it. Granted, it takes 3-4 hits to kill a rat, but it is so safe since the entirety of what’s on your screen is staggered that it’s not even fun. Against shields or armour : heavies do the same.
You can take advantage of the stager system to kill SVs : Heavy (stagger 1) > Push (stagger 2) > Push-attack > repeat and the SV is dead.
See @Rebel’s video for an example of this : GS isn’t that bad against SVs.
For mixed hordes, this allows to clear elites AND thin the horde down at the same time, while most other weapons have to chose between horde trash or elite focus.
Also for reference, here’s the same @Rebel clearing 35 SVs alone with a GS.
Excellent THP on cleave generation, cooldown generation, 10% dodge bonus with 3 dodge count, insane cleave, good stagger… it’s just factually an excellent weapon.
I agree it’s a bit dull in that the lights are 2 horizontal swings and the heavies are 2 horizontal swings with armor sliding, but mechanically it works more than fine.
See this post for exactly the same opinion but from the man who converted me to GS himself - and you can read the entire topic since it is relevant to this one.