Na, sorcerer>monk for solo.
Monk's speed bonus<Haste (which a sorcerer can get)
Intelligence drain only has a effect if it hits you, it won't go through mantle/weapon prot spells (it might be non-magical, in which case you would just use a prot from normal weapons).
The Level drain is a much worse problem since it's permanent, unless your saying that you could play a entire game with only getting hit 1 or two times by a vampire, then i don't see any way to survive.
A monk, unlike other fighters, can't start with a higher strength then 18 (although i suppose a half orc might let you push it up to 19)
Mages/sorc's can open locks with knock (spell).
Yeah, you don't have to fight a dragon till ToB, but i just don't see how you can kill Abazigal without a way to dispel immunity from magical weapons (or surviving the 20 or so rounds till he runs out, but i don't think that that would be feasible with a solo that can't even use any healing potions).
Also, I don't really see how you could go through the whole mellisan battle with only using lay on hands, with healing potions i could see it easily, or with items that give regeneration over time, but without any of those (or a way to completely avoid taking damage), dunno how you could do it.
Edit: Oh, and did I mention that Monks have access to hide, move silently, and detect traps?
Sorcerers have access to detect invisibility, true sight and invisibility.
tl;dr
Sorcerer>Monk
How would you counter level drain?
EDIT:
Perhaps most importantly, i couldn't imagine a solo monk run being anything but ridiculously boring the whole time, due to the complete lack of any strategy (and would just be watching your dude punch them the whole time, especially without using any items)