I'm mostly chalking the dated design of BG1 and 2 to the designers at BioWare rather than the D&D rules, but there are definitely things about the old rules that are just horrific. AoE stuns that last for 10 rounds may as well be instant death when they hit your party (5e versions of the same spells only target 1-4 opponents), and then you get to things like Energy Drain that semi-permanently drain entire levels in 2e but only temporarily drain one stat in 5e; the things that remedy or counter those spells basically require you to know what's around the corner, and the game doesn't foreshadow them.