I think this will ruin the fragile equilibrium of amazing precrowning gifts and disturb the balance of the universe.

No, sorry, actually I think it's a good idea, considering the fact that the only remote use the tome now has can be fulfilled by the guaranteed moon sickle.
Ratling fodder comes to mind too, a redeeming feature, I'm sure.
I still won't read the book unless I have 20 spare scrolls of corruption removal and badly need the spells. Which won't happen anytime soon. Or ever? Close enough.

I don't think, generally, all artifacts need to be great. Having a couple useless artifacts helps stop precrown scummers if nothing else, and adds some variety/rng screws to life

That's an interesting theory :P

On one side I agree with JellySlayer about not all artifacts having to be good. On the other side, the black tome sucks hard. It's probably the one random artifact I wouldn't want to have even in the early game, a point when any of the other ones, even stuff like Black Thumb, would be highly valued. Getting precrowned with it is a quintessential ADOM disappointment. Porkman's suggestion would definitely fix this, while it would still corrupt you.

You can sell the Black Tome for 40k or so. That much money can do a lot of very useful things in the early game ;)

If precrownings are part of the "quintessential" ADOM experience that's a problem in and of itself.

Not all items in ADOM are the best thing ever. I've found some pretty bad weapons.

Let me ask you a question, if you did not know it corrupts what would you think of it? Because a new player doesn't know it does, he'll happily use it, which is the point of the whole exercise.

If you play the game spoiled you miss 80% of the game. I'm fine with the traps set by the creator, it teaches the player to never be over confident and always expect the worst.

This is fine as-is. Variety is the spice of life.