(About Baldur's Gate 1 & 2)
J Lo: Some spells require the mage actually touch their enemies. Their attack rolls are so low that the mage will probably get killed before he can do it. It also means putting your casters in melee range, a position they should never actually be in.
I disagree about the statement that casters should never be in melee range, particularly if we're talking about arcane casters and especially BG2 (particularly Throne of Bhaal):
* Arcane casters can negate physical attacks that would otherwise hit, via Mirror Image and Stoneskin.
* There's also Protection from Magical Weapons, which has a low casting time and makes it so that anything that counts as a magical weapon will not hurt the character. Given that, at high levels, nearly every enemy is using magical weapons against you, this is quite powerful.
* Arcane casters may have low AC, but at higher levels AC stops being meaningful. (This is that problem with accuracy/evasion scaling that I mentioned earlier, but applied to this specific game.)
* The characters you'd expect to be able to survive in melee frequently have AC as their only or primary means of protection, and at higher levels, as mentioned above, that's no longer useful. Even when you do get defenses that mean something, it generally only consists of percentage damage reduction, and won't negate damage unless you're able to stack the effect (and the fixpack and EE creators seem to have a vandetta against effects stacking with themselves).
* Therefore, arcane casters can survive better in melee range than fighter-types can.
(Incidentally, the one other game I can think of where the mage can survive really well in melee range is Star Ocean 3. Give the mage a passive to increase her MP, equipment to regenerate that MP, and there's a way to convert HP damage into MP. Once this is done, her HP no longer matters, and the enemies won't be able to cut through her MP faster than it can regenerate. (For those not familiar with this game, SO3 has a mechanic where some attacks damage MP instead of HP, and if MP drops to 0, the target dies; note that this applies both to party members and to enemies, so sometimes it makes sense to MP kill enemies rather than HP killing them.))
J Lo: The Enhanced Edition added the cavalier to BG1. The kit gives +3 vs dragons and demons. There are no dragons in the game, and there are only 3 demon encounters. By the time you get to them you should have enough gear, spells, and levels that this won't make any material difference.
Pathfinder: Wrath of the Righteous has a similar issue. There's a druid archetype, Defender of the True World, that gets some bonuses when dealing with fey. Unfortunately, there's practically no fey in the game (not counting any that are summoned by the player), and as a result this archetype is almost useless. ("Almost" because you at least get cold iron natural attacks, and some demons have damage reduction that cold iron can bypass.)
(With that said, note that this archetype is useful in Kingmaker, and is generally preferred over vanilla druid, simply because fey are common and dangerous in that game. I believe the only reason that archetype exists in WotR is that it was in Kingmaker and Owlcat didn't remove it when making WotR.)
J Lo: Baldur's Gate 1&2 have a save vs polymorph stat. There are many enemies in each game, and not a single one will try to use polymorph on your party.
Reminds me of FF6 (SNES and PSX), where the Evade stat is useless, because it's the MBlock stat that affects your chance of dodging physical attacks.
This also makes many effects that are supposed to help with evasion, including many shields and at least one relic, pointless. Furthermore, the blindness condition has almost no effect; all it does is prevent the character from learning blue magic, and there's only one character (out of 14 permanent characters) who can do that.
The GBA version changed it so that evasion now works the way you would expect.
Related: In SaGa 1, confusion is useless for the player. A confused enemy will continue to attack you, and if the enemy uses a melee attack, instead of just hitting one character (probably the first one), it will hit the entire party! When they ported the game over to the WonderSwan Color, they did not fix this bug. (There's many other broken game mechanics, like a certain saw that, if used by a strong character, might fail except against two specific enemies. With that said, that saw is still worth having around even if it's only going to work on those two enemies.)