Speaking specifically about the Greatswords that Saltzpyre and Kruber can use; these weapons are bad. When they got their cleave buff (the ability to cleave through anything) and their new push-attack that finally gave them some anti-armor damage, they went from “boring garbage tier” to “meme tier”.
And on top of that, they’re just boring to use. Both lights and heavies are only wide swings, with only the push-attack giving some variety.
So what can be done?
Frankly, these weapons need a re-think. While greatswords were definitely real weapons, their heyday in actual warfare was relatively brief, and we don’t have a great idea of how they were used on the battlefield. There are some sources that suggest that they were used against pike blocks, but we don’t know how.
Then, we have the fantasy version of Greatswords, which grow to comical proportions and become massive, clunky chunks of steel that can destroy anything but take five minutes to swing.
That’s not really accurate, and Vermintide seems to veer a little more towards realism here; but notably, in historical records, Greatswordsmen were paid double of normal infantry, and these being elite weapons carries into Warhammer. Their elite qualities in Total Warhammer are counted as them being both anti-infantry specialists and having armor-piercing. In real life a big sword is not any better than a regular sword at piercing armor (as in, it does not at all), but we’re following the Fantasy Rule of Cool here, that a bigger sword can cut more.
So here are a number of suggestions;
Give Greatswords light AP on light attacks. We’re talking comparable to the Glaive, perhaps slightly weaker. Glaive lights take dozens of hits to kill a Stormvermin on Cata, but at least you’d be doing something more than staggering as you cleave through a mixed horde. The AP on standard heavies can be upped as well if necessary, but just slightly.
The weapon does need a way to deal with armor seriously, though. So give it a new special attack where you grip the blade (halfswording) and stab with the tip. Not great range, but good AP damage against a single target. There can be a short combo of these stabs to allow some follow-up hits. If aimed well at the head, these attacks should cause serious damage to Stormvermin on higher difficulties. As a neat little bonus, if you block and do a push while halfswording you get a stronger push - having your hand up the blade gives you more leverage (though after the push you revert to normal grip).
Another idea, and I think an enjoyable one, would be to give the weapon a super-heavy charged attack in the same vein as the Pickaxe. This would still be a horizontal swing, but there’s a momentum forward with the attack, and it deals heavy stagger to everything hit, and good AP on the first target hit. This is a full-power, almost out of control swing with a noticeable recovery, but it’d be a good opener against an approaching horde, a solitary Chaos Warrior, or a group of Stormvermin. Even make it open up Shieldvermin on the one hit, giving it some utility for your allies.
Finally, the weapon could easily get some kind of riposte mechanic on its blocks. (@OrsonMaxwell’s suggestion).
Even if all these changes were implemented, I don’t think the weapons would be meta - it would still not be great against armor, it would still be slower than most other weapons - but it would be cool and definitely usable. And isn’t having a giant, awesome greatsword something we all want?