The entropy doesn't change the chance of guessing one seed phrase compare to another.
Yes, it absolutely does. If I have 256 bits of random entropy sourced from /dev/urandom, and you have 256 bits of entropy sourced from your browser fingerprint, then your seed phrase is exponentially weaker than mine and exponentially more likely to be broken.
Are there 24 words combination from words listed in BIP 39 protocol easier to guess than other?
Yes. It all depends on the entropy used to generate those words in the first place.
As there are 2048 words, total number of combination is 2048x2047x2046x...x2025x2024.
There is nothing preventing repeat words, and the last words contains a checksum, so as above there are 2
256 combinations, not what you have written.