A. The PCs weren't constantly one failed save away from death.
I wish this wasn't true. There aren't enough long-lasting good defense spells. Opponents usually have low save DCs (check out the save DC of a titan's spell-like abilities), which isn't a problem if the opponent can dish out
disintegrate every round but is a problem if an opponent wants to dish out
hold monster every round.
B. PC wizards got enough spells that they could afford to spend the 6 or 8 high level spells/encounter that DMs seem to require before the encounter is "fun."
They can at 20th-level ... where did 6 or 8 come from? The typical encounter is supposed to last 5 rounds - not 1 round, and not 8 rounds.
C. If disintegrate really did result in single spell battles. The iconic example of this compaint seems to me to be Wizardru's Winterwight succumbing to a Disintegrate in round 4 or 5 of the combat (After the PCs either failed to beat his spell resistance or he saved against every other spell that had been tossed at him). My experience with Hold Person (which regularly receives similar complaints) is the same. For the one time, it enabled a 4th level party to defeat the fiendish evil cleric in round 1, there were ten or eleven times that the enemy made his or her save or that taking out the one foe left seven others alive and kicking. PCs with huge strengths, Keen scythes and improved critical, generate similar one round combats whenevery they crit yet nobody complains about that. I see disintegrate (and hold person) as being roughly in the same category.
Sure, if the DM goes out of the way to create a creature with really good saving throws, such as a cleric (good Will save) who is fiendish. (A fiendish cleric is an outsider, and is immune to
hold person in any event.)
In any event, that winterwight example looked like it was actually a challenge. That would be more fun for me as a spellcaster player, rather than "oh look, it's CdG bait".
Or you can add spellcasters
to every encounter so you have someone who can cast
remove paralysis or
freedom of movement - but then you end up with ridiculous scenarios. ("That tribe of giants has a high level cleric? The one in the black hat, right?")
Not every monster has the ability to cast
death ward or other countermeasures that the players have.
Furthermore, the complaint was about
high level - not 4th-level.
PCs with huge strengths, Keen scythes and improved critical, generate similar one round combats whenevery they crit yet nobody complains about that.
Sure they do. DMs complain endlessly about high-CR monsters having such wimpy AC scores. If they had better AC scores then the PCs
wouldn't be able t o kill them in one blow - at least not on a regular basis. Ever wonder why so many DMs hate vorpal or
polymorph other?