I think true brokeness in this case is not so easily showed by a simple smackdown, especially with the loss of 3 spells/round (haste revision).
Most smackdowns are based around a single character dealing as much damage as possible in the shortest time possible, but that´s not what this character can do better than any other smackdown caster...
But it becomes interesting if you see the MT within a group that works well together.
He can cast several 2nd level statistic boosters, 1st level Blesses, and 3 to 4th level Greater Magic Weapons.
If you have a sure access to Bull`s Strength, you will never bother buying Gloves of Ogre Power, and probably not even a Belt of Giant Strength +4, because the caster will guarantee this to you. So you can buy more unusual but powerful equipment, that gives the group as whole more (fire)power.
While a normal Cleric/Wizard could still do this, he would not have many higher level spells that can help the group...
A single classed Cleric or Wizard can never do this, but he has access to higher spells and has a better caster level.
The MT now still has some high level spells (even if not as high as a single classes caster), and he has more spells on a given level than a single classed character could get (at same character level).
In a normal group, the procudure would be like this:
1. At morning, Cleric and Wizard buff everybody.
2. While fighting, Cleric wades into melee, WIzard casts powerful spells against enemies.
3. After combat, Cleric heals the rest of the characters. (Usually via Wands of Cure xyz)
the same thing, but we replace the Cleric and the Wizard with a single MT.
1. At morning, MT buffs everybody in the group.
2. During Combat, MT throws powerful spells against your enemies.
3. After combat, MT heals the rest of the characters. (usually via Wands of Cure xyz)
You see, in situation 1 and 3 the MT acts as 2 characters (maybe the durations of his buffs don`t last as long as the 2 characters, but the numbers per day are nearly the same, once the MT has access to it...)
In situation 2, he only acts as a single caster, but that`s normal for a single caster and not a weakness. still unaccounted there, the MT has a far greater variety in his spells, though he will probably rely more on the Arcane ones, because they deal more damage and the MT`s BAB and Hit Dies avoid him using Cleric Melee Tactics
(But this frees his Cleric slots for later healings or "rebuffing" or maybe castind Augury and Diviniations or whatever else you think of...)
Mustrum Ridcully