[Update #2]: The next big bug-fixing patch is scheduled for early July.
[Update]: The newest beta update has greatly beefed up Orcs and their Black Orc Big Boss hero.
Total War: Warhammer 2 just recently added The Warden & The Paunch DLC alongside a massive Greenskins rework. The rework made it so Waaagh! armies are now significantly more fun to manage, scrap has been introduced as a new means of upgrading Greenskins troops, while the new tech tree ensures that even the lowliest goblins can become viable in the end-game.
While all of that is certainly a solid addition, the update unfortunately brought with it a rather sinister bug as well - any additional weapon strength is simply not being counted. So if you're wondering why Grimgor with his 900 weapon strength seems to be struggling to beat up a skirt-wearing Empire wizard, that would be your answer. He and the other units are permanently stuck on their initial weapon damage, and no matter what items, Waaagh! buffs or events that pop up, they will never move from that number no matter what the unit card says.
Needless to say, this is an absolutely devastating bug for any sort of melee-centric armies, both for the players and the AI. As such, I am also happy to say that a fix is now available as a part of a new beta update on Steam.
Simply head on over to Total War: Warhammer 2 in your Steam library, go into its properties, and from the beta drop-down menu select “warhammerii_1.9.2." Your game should immediately start updating to the new beta version, but if it doesn't, simply restart Steam and it should work just fine.
As far as compatibility is concerned, the beta update should work perfectly well with any current save files given that it only fixes the weapon strength bug. So if you're in the midst of a Greenskins campaign, hopping into the beta is highly recommended given how much the faction relies on melee units!
Have fun, and here's to hoping the fix goes to the live servers in the near future as well.