Heh... You just exactly described our high level 3.5 games.
Thankfully, we all play 4e now.
I've told this story before, but, hey, one more time.
A "Typical" Round of our last 3.5 20th level game.
PC 1: Wizard/Loremaster: Cast
Bigby's Clenched Fist. Check SR. Make attack roll with Clenched fist. (+20 for CL, +11 str, +7 Int mod, -1 Str). Roll damage (1d8+11) and target rolls Fort save vs. Stunning. Then casts
Quickened Magic Missile, Checks SR 5 times, 5 1d4+1 missiles. Then directs his 1d3 summoned, augmented huge earth elementals to make full attacks (2 attacks, +19 melee, 2d10+9.
PC 2: Cleric 20: Reminds everyone of their vigor spell (everyone gets 4 hp back. Uses Divine Power to up his caster level (turn check) then casts
Cometfall, 20d6 damage, Reflex 1/2. Moves. Else, Casts
Heal or
Mass Cure to save Ranger, F/W and/or Rogue.
PC 3: Wizard/Arcmage: Begins with Polar Ray (20d6, ranged touch, checks SR). Uses
Quickened Targeted Dispel Magic on Foe, rolling a CL check for each of the foe's buffs. DM recalculates foes stats. Moves.
PC 4: Ranger 20. Makes 5 attacks (4 bab, +1 speed) with +4 speed bastard sword, rolls damage (DM subtracts DR and notes), and rolling for three attacks with off hand (+3 cold iron holy shortsword) again doing damage and DM subtracting DR.
PC 5: Rogue/Thief Acrobat. If its sneak-attackable (which is rare) 5 foot, (to flank with ranger) make three attacks with primary hand (each doing 1d8+5 +8d6 SA) and one with off hand (doing 9d6 SA). DM notes totals and subtracts DR. If not, hang back with my shortbow and do three attacks at 4d6 (fire, holy). DM checks DR and Energy Resist.
PC 6: Fighter/Wizard/Eldrich Knight/Arcmage. Arcane Strikes with full attack for a +9 to hit, +9d4 damage on four attacks. DM notes, subtracts DR.
Quickens a magic missile (checks SR, 5 1d4+1) for good measure.
Enemies Turn.
While in theory someone was typically getting shafted a full attack round (moving, etc) each PC's turn had at least three distinct parts, many had up to seven or more. It also assumes around round 3 or higher, rounds 1 & 2 were typically full of charging, the casting of haste and mass animal buffs, dispelling enemy buffs etc.
No wonder it took nearly half-an-hour to play out one round of combat...