Zardnaar
Legend
Others have covered it a bit, but just in general, having species, class and other modeling options that can produce PCs that vary significantly from the pre-2Ed editions.
While AD&D introduced some new classes & races, 2Ed took the first major steps with introducing kits, then vastly expanding race options with the softcovers. Then the Player’s Options books arrived…
And 3.X expanded upon that.
After more than 45 years in the hobby, I’ve played most of the stereotypical race/class combos from pre-2Ed that lingered on even afterwards. So when I sit down at a gaming table to start a new D&D campaign, I have those character concepts ready to go and can generally create one pretty quickly- I’ve even played some in 3.5 while I was still generating the character (I was late for the first session). But I’d much rather try something askance from the same old same old.
So being able to create and play things like a full caster in heavy armor, a “Paladin” with arcane spells, or a 2-headed bipedal fey dog-man engages my creativity at a different level. I invest more in the PC.
Ah rgr.
In 5E if you're proficient in armor you can cast in it.
Paladin with arcabe spels doesn't really exist. An arcane "paladin" it either a hexblade warlock or multiclass Paladin/Sorcerer. Hexblades also a popular dip eg hexblade 1/Sorcerer XYZ.
The charisma based classes multiclass really well togather.