The biggest issue though is simply the sheer number of spells casters get in later era D&D. Remember, your 3e wizard (or later) is getting bonus spells at each spell level (probably up to 4th in 3e) and can recover spells during the day without resting. Plus, since 5e makes all casters basically sorcerers, you don't need to lock in slots. You can have fireball and Leo's Hut, and if you don't need the Hut, you can just fireball again. Plus, with upcasting, you can simply burn that 3rd level slot on a 2nd or 1st level spell in a pinch.
Of these issues, IMO upcasting is the problem one.
I don;t mind casters using the 3e Sorcerer mechanics in that over the years I've come to loathe pre-memorization. The counterbalance, though, is to limit how many slots per level a caster can have (and no at-wills!) and have it that a slot can only ever be used to cast a spell of that level.
I've run it this way in my current campaign and thus far learned the following:
--- pro: at low levels I saw spells cast that otherwise would never see the light of day
--- pro: casters are more flexible without gaining too much power, again at low levels
--- con: it still doesn't fix over-power problems at higher levels (i.e. about 6th+ in my game) as I didn't restrict slots harshly enough
--- con: at higher levels the same few spells are still by far the most commonly cast
The first 'con' is easily-enough fixable for next campaign (I'm stuck with it for this one) by just reducing the number of slots gained per level. The second 'con' would be much harder to fix in that I really don't want to put a restriction on how many times each individual spell can be cast in a day for two reasons: it would be a bookkeeping nightmare for the players (and me, for NPCs or foes), and it would cut back on flexibility - the very thing I'm trying to promote.
Keep in mind also that in my system there's other balancing mechanisms in play, the biggest one being that spellcasting is easily interrupted and an interrupted spell can sometimes have "interesting" side effects due to wild magic.
It was far more common in AD&D for casters to have unspent spells all the time. And the opportunity cost of taking spells that were more limited use just wasn't worth it.
Yes, and this led to casters - no matter how many different spells they had available - always memorizing the same core few. I specifically wanted to get away from this, but as noted above the results have thus far been mixed.
OTOH, in 5e, I am seeing spells being used that I had never seen used in D&D before. Heck, our Cleric just cast Control Water and the group was nowhere near a boat. I'd never seen that before.
Nice!
