Thief THAC0 question

[stone]

I saw this in a guide and I can't work out the reasoning behind it. Why would delaying training until the

Spoiler

lower ward

result in more THAC0?

"It may be nice to postpone becoming a thief until we reach the

Spoiler

Lower Ward

. This would give us a better THAC0 for the rest of the game
at the cost of some more trouble during the

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Tenement of Thugs (you
would probably need to use Annah to skip by the thugs),

and it takes a
little more time to train as a thief at the

Spoiler

Lower Ward

. On the other
hand, it will probably facilitate all fights. All in all, this seems
like a judgement call"

[GawainBS]

You get more Fighter levels earlier, but I don't see the overall THAC0 reduction, since you can grab those levels anytime, even at the same XP cost. Consider that advice in the guide invalid. (Unless I'm missing something as well.)