Corvettes: Vincent, Zechitinu, and even Inazuma is pushing it in my opinion
Destroyers: Essex or Whirlwind
Frigates: all seem fine to me
Cruisers: all seem at least okay to me
Heavy Cruisers: Agamemnon, Sovetskii Soyuz (also seems under-gunned for the Heavy Cruiser designation, not sure why this isn't designated a transport or cargo vessel)
Battlecruiser: Cameron seems a bit light on the armor for a battlecruiser, but I've never used it, even in previous rule sets
Battleship: Mckenna (and pretty much all the "Lost" battleships) The McKenna is a good ship, but it has less than half the armor tonnage it could have without changing it's speed or SI... I think that is a poor choice for a battleship design... even if it has the firepower to not need to worry about that too hard against most ships.
First off, anything designed after the Succession Wars has to be looked at with the understanding that everybody that knows what they're doing has been dead for
three hundred years. Hideously flawed designs are the expectation, not the exception.
Vincent: You should check out the WSotW article down in Fan Articles. It's a corvette, which means its job is to be a wide-ranging early-warning platform that
might be called on the intercept or harass light forces approaching your real combatants. Engaging other WarShips is not in the job description, thus there is no need for it to be armored as such. Moreover, it's actually one of the toughest corvettes of the pre-Clan eras, obviously ignoring anorexic destroyers like the Mako. The TRO can say what it wants, that ain't a corvette.
Inazuma: I'm not seeing the issue here, that thing may not be a brick, but it's plenty tough for a corvette, especially one that's designed solely for high-speed engagements.
Zechetinu: Another ship whose job description doesn't really call for fighting other WarShips. On the other hand, I will grant that in the ages of genuinely scary assault droppers, PWSes, and XL-ed heavy fighter wings, the Zech is kinda thin-skinned. Oh well, somebody has to be on the bottom of every totem pole. Best advice I ever saw about the Zechetinu came from its WSotW thread:
An important lesson there for everyone.
Use a unit how it works. Not how you think it should work.
It saves a lot of heartache.
Really, that should be applied to all WarShips.
Whirlwind: Again, not seeing a problem. The Davions saw them as a failure, so flaws are to be expected. They're actually pretty tough by SLDF standards, and one look at the weapons loadout tells me this ship is another built solely for high-speed engagements, not the extended slugging matches that call for a thick hide.
Essex: Yeah, this could be tougher, though it compensates with a fairly high SI.
Agamemnon: Definitely could be tougher. See the recent "Talk to me about..." thread about it down in Fan Articles. Remember again, WarShip design experience was completely lost for three hundred years, leading to the same mistakes people made in real life. The Agamemnon is a WWI British battlecruiser in every way that counts, with all the strengths and weaknesses thereof.
Sovetskii Soyuz: You know the bit about most naval stations being assigned a couple garrison fleet destroyers, and occasionally a cruiser? Pretty sure those cruisers are almost always SovSoys. Built when the SLDF felt the need to massively expand the number of hulls in the fleet, but likely had to do it on the cheap(relatively). SLDF battlecruisers are meant to be third-rate battleships, and in the same way I see the SovSoy as a third-rate cruiser, meant to give you a hull big enough to make the Houses and pirates think twice about shenanigans, but cheap enough to be deployed in places that don't merit a Luxor or Aegis, or even an old Avatar. Quite literally, it is quantity over quality.
Cameron: This class is an explicit failure, with all ships related to transport duties. With that background, I'd say it's actually a surprisingly potent design.
McKenna: It could mount more armor, but does it need to? It's a broadside fighter, so nose and aft about only need to keep you alive long enough to shoot the helmsman and replace him with someone competent. As for the sides, consider this: By and large, the gold standard for a heavy capital bay is the quad HNPPC turret. It can do a LOT of damage with a normal shot, but can also be bracketed down for very good accuracy at extreme ranges. The McKenna is designed with in mind, built to fight at ranges where other ships cannot respond. If they don't have big bracketing bays, they're missing shots too often to kill this ship before its own guns pick them apart. If they do have the ability to bracket like a McKenna, then those quad heavy peeper bays are doing 24 damage. The McKenna's broadside armor belt is too thick for a 24-point hit to threshold. Coincidence? Real-world, certainly. In-universe, I highly doubt it. :)
The Battletech universe makes a lot more sense if you assume that in one way or another, spacecraft armor is by far the most expensive part of the ship, and that shipwrights only ever put just as much as they think the ship needs, and no more.
(Disclaimer: I don't care one whit about C-bills.)