Blackbeard: The Blackbeard's representation is tonally at odds with how it's most optimally used. So many people see it as the Berserker Attack-Attack-Attack mech because of SEKHMET when it actually rewards a very measured, considerate playstyle of grabbing enemies, shutting down their reactions and moving them out of position.
Raleigh: The Raleigh has a niche that it comfortably occupies now, but I feel like it's illustrative that it didn't find this niche until the Stortebeker came along and provided the power fantasy that everyone thought they were getting with the Raleigh the first time they saw it.
Tortuga: Cool you made The Mech That Is Good At Everything and its literal only weakness is it's a bit slow, one of Lancer's easiest problems to fix? The Tortuga is without a doubt my favourite mech and even I think it needs to be nerfed a little.
Vlad: The Vlad is an all-around excellent close combat frame hampered by a slightly unfocused and lackluster toolset. What is the Impact Lance doing here? Why would I ever use Webjaw Snare?
Black Witch: "My core power is that if my ally is a CQB mech like the Tortuga, they get to do no damage for a turn and then eat 6d6 damage to the face." Mag Field is so easily circumvented by just not firing into it - or, if a PC is inside it, firing into it a bunch to pump its damage. Also for a piece of pinnacle gear that costs 3 SP, Black ICE Module just... doesn't have enough punch.
Death's Head: As Zee Bashew would put it, "I get to spend one whole turn imagining how hard I'm going to hit this enemy instead of actually taking the turn to hit this enemy." You have to spend your entire turn focusing on an enemy for the potential to roll a ton of extra damage if you crit. Remember that the Railgun, the Death's Head's signature weapon, is an area weapon and bonus damage is halved for multi-target attacks. The enemy can also shut off this extra damage by being in any form of cover. Bad core power. Possibly the worst.
Goblin: So I get to spend a Quick Action to lose my action economy and get my friend and I heatgunned and AoE'd to death? And it ends if either of us get Stunned? And this is what I have to spend my core battery on?
Hydra: Hello yes I am The Mech That Procs Twenty Bazingillion Saves, which is why my Save Target is the lowest possible starting Save Target in the entire game. Also my action economy is consumed by handling all these drones but I also have to be an off-striker for some reason!
Manticore: I wish they'd never put that fucking meme trait on this thing. I never fucking hear the end of the stupid fucking LMAO EXPLODE jokes.
Minotaur: Genuinely, what is the power fantasy here? I look at the Minotaur and I struggle to understand what precisely I'm supposed to be imagining myself doing when I pilot it. Couple this with a powerful equipment package, but on a frame that doesn't feel fun or interesting to play, this is a license you dip into to get something important for a completely different frame.
Napoleon: So I can spend my core power to just not play the game?
Saladin: This frame has the opposite problem to the Minotaur. It has a very, very clear power fantasy - "create a bubble of impenetrable safety for my friends" - and goes absolutely hard on it. You then discover that being permanently immobilised or slowed and having to spend most of your actions maintaining the bubbles with very little else to do is miserable. The power fantasy is so well-defined you end up discovering why it's not very fun.