Willie the Duck
Hero
There certainly was variation in how powerful casters were based on how easy the DM made it for the party to exit the dungeon and rest up/recharge their spells (making it campaign dependent). It's worthwhile to note that, for AD&D (in particular and in comparison to some in the basic-classic line), spells didn't recharge 'daily' so much a 'daily, plus whatever free time and safe situation necessary to sit and recover spells at a rate of 10 minutes per spell level recovered,' making the whole proposition or 'resting to recover spells' a lot more of a logistic challenge (and thus potentially part of the fun and engaging portion of the adventuring process). So it really starts to get apples to oranges with AD&D specifically.Was this a problem in AD&D though? I don't ever recall it being an issue, but then again I have never felt much issue (if any) with the martial vs. caster disparity.
However and regardless, broadly speaking it is specific game changes between the TSR and WotC era that facilitated this. In particular, the muting of Vancian limits and thus being able to bring most spells to bear in any given encounter.
- 3E had full* Vancian casting, but easy and ubiquitous scroll and wand magic item making/buying rules means you could have the wand of cure light wounds to heal up after fights and scrolls of knock or passwall for those hyper-specific dungeon-crawling scenarios that came up, leaving your daily memorization loadout for reliable encounter-addressing spells. *yes, yes, there are subtle differences between the way things work in Vance's novels and how it does in D&D. You know what I mean.
- 4E had the AEDU system, ritual magic, and purchasable magic items. The specifics are different from 3e, but this too results in generally entering encounters with spells at the ready (or even encouraged to be used, in the case of those that recharge every encounter) appropriate for the situation.
- 5E has the quasi/post-vancian system where you have an overall limit, but still get to swap out sleeps for magic missiles for detect magics (if not cast the latter via ritual).
Now how often actual gameplay meets that theoretical outcome is just as unclear as it was in the AD&D era.