I never see them over the other missile units. Archers are cheaper and Huntsmen are just better. Plus those two have loose formations while crossbowmen don't.
Might have included River Trolls here as I don't think I've seen them once since the DLC. Stone Trolls just outclass them both right now. But Trolls just feel like they don't generate value. I understand the concept that they're supposed to somewhat function like Skaven running away only to rally and come back regenerating the entire time. It just doesn't work at high level play though, there is always something that will chase them off. Or they'll simply shatter after breaking 3 times.
Dwarfs: Giant Slayers
I'm not actually sure if they're bad or not but I never see them brought over Slayers. They're more expensive than Hammers but extremely squishy. Complete glass canons. But the bigger problem is they don't have bronze shields like regular slayers so they get completely wrecked by missiles with their 0 armor. For something more expensive than Hammers?
Vampire Counts: Cairn Wraiths
Costs the same amount as Grave Guard with half the HP. Would be okay if magic damage wasn't so abundant in every race.
Warriors of Chaos: Chaos Trolls
I think trolls are in a pretty horrible spot right now. Base 40 leadership is abysmal. It would be so bad if it wasn't for the fact that unlike the AI any decent player makes sure to chase off routing units. They almost never make up their cost. And they terror route.
Bretonnia: Foot Squires
I'm a little out of my depth but I feel like Foot Squires are a waste of an investment. They wont beat elite infantry or even do that much damage to them and its generally better to save your money for expensive Cav and go wide with far cheaper infantry backed up by a Reliquae
The other Giants almost made the list but I genuinely think Trolls are worse. Giants at the very least are great at fighting monsters. Except this giant is completely overshadowed by the Cygor who is basically a giant that doubles as an artillery piece. I can't remember the last time I saw a Beast Giant.
Wood Elves: Great Eagle
Nothing controversial here. Its squishy and its animations are terrible for combat as is its DPS. Its basically a worse Manticor, which it shouldn't be since it costs the same amount.
Norsca: Norscan Trolls
Ice Trolls could probably fall in here too. I think frostbite gives them a little more utility for punishing sloppy lord positioning. But regular trolls just never seem to do anything. Even saturated among Marauders.
Dark Elves: Cold One Chariots
A chariot unit that Rampages. Even if Scourge Runners didn't completely outclass them in every way they still wouldn't be worth bringing at the insane price of 1100. They should be cheaper than Scourge Runners if anything.
High Elves: Great Eagle
Same as Wood Elves compounded by the fact that Phoenixes are actually good.
Lizardmen: Ancient Stegadon Engine of the Gods
That spell is definitely not worth the insane premium you pay for it. Even Arc of Sotek I expect could generate more value. At least you can get 2 of those for the price of 1 of these.
Skaven: Storm Vermin Halberds - They're just not good enough for their price point. Regular Storm Vermin could probably use a price reduction too but at least they are actually good at killing infantry. These guys just have too big an opportunity cost for no utility. No one uses them to take down Cav or monsters they use their missiles, artillery or monsters. They're simply there to protect those units and for their cost you can get 3 clanrats or 6-7 Slaves.
Tomb Kings: Nehekara Warriors
Every time I see these guys brought I always see them taken out by almost anything, they're super squish and don't have anywhere near the staying power of spears or killing power of Tomb Guards. There is just no reason to bring them over those options.
Vampire Coast: Depth Guard Polearms
Same problem as Skaven but time 10. First they're actually more expensive than Depth Guard not less which is insane and second like the Skaven their role is better filled by missiles, artillery and monsters.
Request scorched body textures, poisoned dying animations for infantry's skeletons, a blood slider that allows us to control how much blood appears in battle and make proper death animations for all ethereal units so they vanish for Blood for the Blood God 3.