Also in a 12 or 24 word seed phrase, if only one word is missing, it would take the same time to brute force it.
This is wrong.
If you miss 1 word in a 24 word seed phrase, there would be 8 possibilities for the missing word on average.
If you miss 1 word in a 12 word seed phrase, there would be 128 possibilities for the missing word on average.