I would vote for feral druids as having the highest "type-A skill floor".
Ferals do mediocre damage unless you know to pool energy for FB to double its damage and provide a druid's only burst. Ferals are also incredibly easy to kite when they don't know how to powershift or when to root, which lowers their damage further. Ferals come with pathetically weak heals that are very tempting to bad players, but which should actually be used extremely situationally. And several of the control/defense/utility abilities a druid has are not very intuitive or easy to use correctly (shadowmeld, warstomp, roots, thorns, bear form, travel form). Even stealth is pretty easy to wrong, since druids move slower in it and don't have any ambush. You can waste a lot of time-on-target by chasing after someone who doesn't even see you, when you should be dropping stealth and chasing them at 130% speed (depending on the class, ofc, don't do this vs hunters).
Ferals are also reasonably easy to spec incorrectly thanks to the deceptively bad* Predatory Strikes talent in tier 1, which might seem better than Furor. Ferals are also deceptive to spec due to the three weaker damage-increasing talents in tier 2 that superficially appear better than the subtly powerful 25% snare.
Lastly, feral damage is fairly weapon-dependent, and a druid that doesn't know to beeline for the highest possible weapon dps before other upgrades is underplaying the class is a fairly substantial way. This isn't a huge overall effect, but it's significant because very tactically smart players could be entirely unaware of the pve/theorycrafting importance of weapon dps for calculating druid autoattacks (and therefore mangle), and have no idea they're doing 10%(?**) less damage than they should be.
So it takes a pretty big skillset to make feral effective, because the feral playstyle, talents, and even weapon choice are all pretty counter-intuitive and loaded with easy pitfalls for players who don't know what they're doing. As a result, a poorly-played feral druid loses to pretty much every class, and often without doing much damage before dying.
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* I've seen people debate this, and I am by no means experienced enough on my druid to really say (Shft assures me that the talent is crap). But even if you think predatory strikes isn't "bad", then surely you at least agree that it has a massive skill requirement, and is a bad talent when used by a bad druid.
** 10% is a wild-ass guess, I have no idea how much it actually works out to. At lv 60 and below it's supposed to be the biggest single source of damage upgrades for ferals, and at 70+ feral attack power takes over for damage scaling purposes. The amounts of FAP (lolz) on level cap weapons should give a good idea of how big a deal weapon dps is.