jasin said:
But how about addressing the point the example was meant to illustrate: a healthy 20th-level wizard in his prime (so Str 10, Con 14?) will probably be able to kill, bare handed, an armoured and armed trained warrior (say Ftr1, Str 15, Con 14?). We learned to accept this as natural, because, hey, he's 20th-level, he's an awesome legendary hero, even without his magic.
That wasn't the point being illustrated in the slightest.
Someone came out and said "I think it's fair to tell the ancient crippled wizard that he simply cannot make that jump check". Someone else came back and said "then why can he make that reflex save, dodge the orc's greatax, or hit the fully armed and armored knight in melee combat?". I asked why on earth the wizard would even try to hit the knight, and someone came up with the ridiculous example, which I then proceeded to debunk.
Now, onto YOUR example, using your stats (except I'm going to bump their 15's to 16's and their 12's to 10's, because that's generally what I see people do with 25 point buy).
A level 20 wizard with 14 con is going to have, on average, 91 HP. The level 1 fighter with 14 con is going to have 12 HP.
The wizard has a +10 to hit, but -4 because he's attempting to deal lethal damage with his bare fists. He does 1d3 damage (avg 2) per hit. He has 10 AC.
The fighter has a +5 to hit (weapon focus is reasonable) and does 1d8+3 damage (avg 7.5) per hit. He has a 19 AC (4 scale mail, 1 dex, 2 heavy shield, 1 shield specialization, 1 dodge).
The wizard gets 2 attacks per round and needs a 13 to hit. He thus averages 1.72 damage a round counting crits; he needs 8 rounds to knock the fighter into the negatives.
The fighter gets 2 attacks per round (AoO) and needs a 5 to hit. He thus averages 13.2 damage a round counting crits; he needs 7 rounds to knock the wizard into negatives.
Amazingly, the fighter wins.