Anyone have any good recommendations on good traps, npcs, or monsters to use against this kind of character?
Fundamentally (IMO), what you need to do is be able to challenge each character's ability to contribute, not be able to take them out*. So the question becomes
'what does the paladin actually do?' From what we've heard, it sounds like the answer is 'survive really well, and grapple fairly well.' Neither of these actually accomplish the goals of the PCs, excepting that they need to be alive to do so.
*without having long ago taken everyone out. As the DM you can always take out the PCs.
Beyond survive, Sorcadins of the PC's level/distribution are known for some decent burst damage (using up the same spell slots needed to survive), and some mid-level healing/curatives. They can't cast
knock, or
spiderclimb, or
see invisible, or have expertise in 4+ skills, or even dish out damage like a Sharpshooter/Crossbow Expert/Archery FS battlemaster or the like. Sounds to me like there is plenty of opportunity for everyone else to leave the Sorcadin in the dust, contribution-wise, if you structure your adventures appropriately.
Even in combat, this character seems likely to be limited to dealing a lot of damage only in constrained situations (burst damage, but also melee, and without the
fly spell). Throw up some difficult terrain, add in some other effects which reduce speed separately (
Plant Growth and
Spirit Guardians are out, but knockback/speed reduction effects and actual obstacles are still options). All of a sudden the sorcadin looks like a traffic pilon shooting 16-casting-stat firebolts while the above-mentioned archer is nearly unhindered and the monk or barbarian or heck any SAD character who has the ASIs free for things like mobility feat all are outperforming them.
I would be very hesitant to continue playing with a DM who thought "armored character + shield spell" warranted a conversation about banning.
Given how un-overpowered the Eldritch Knight is (particularly given how limited 1/3 spellcasting advancement ends up being, to say nothing of the school constraints), I agree on that front. Situations like wizards taking a 1-level dip into fighter/cleric/artificer for med/heavy armor and shield proficiency I am a lot more dubious over.
I'm not certain that balancing MUs by having them very powerful, but very fragile worked perfectly pretty much any time past 1974 (or at the very least it zigged and zagged in effectiveness with every supplement and edition/version). That said, if you are going to include it in the play balance, being able to ameliorate so much of it with as minor an expenditure is noteworthy. It isn't
the reason for the wizard supremacy perceptions, but it certainly doesn't help.
Sorcadins are kinda halfway between. If you think of them as borderline broken, then the heavy armor and shields and
shield is certainly part of it. Personally, I think they are kind of paper tigers* -- they sure
sound good, and
look good on paper -- but when you line them up against a pure** paladin or sorcerer (or fighter and wizard). There seems to be a lot of stretches where you are waiting for next level and your combo to finally kick in while they have multiple attacks or 3rd level spells or such.
*particularly when in campaigns when other options are not as constrained as this 2nd-level-spell ceiling.
**or possibly 1-level dips and the like.