Consider a password consisting of random words each chosen from a 4k dictionary. Say you choose 10 words. Then your password has log_2(4k)*10 entropy.

Now consider a validator that tells you when you gets a word right. Then you can guess one word at a time, and your password strength is log_2(4k*10). Exponentially weaker.

You're constructing the second scenario and pretending it's the first.

Also in your 50% probability scenario, each word is 1 bit, and even 50-100 bits is unguessable. A 1000 word key where each word provides 1 bit would be absurdly strong.