Word count

Hello Rabbi. I am very interested in Chazal’s sermons, and most of them are more or less understandable to me under a metasystem of assumptions about reading the text (such as “there is nothing superfluous in the Torah”) from which the rules of demand that are familiar to us emerge (which have several points of disagreement due to the ambiguous definition of terms, such as “superfluous”). There is only one very central thing that I have not understood until now: what is the idea of ​​places where certain laws are demanded based on the number of words that a certain word appears in the text? On the one hand, it seems that this is mainly an attempt to justify in retrospect accepted and conventional laws whose origin is unclear (toward the end of the first chapter of Sanhedrin, for example, we are left with a question about Samuel, who offers a source for dedicating land in Tisha and Kohen, and it does not seem to bother anyone). On the other hand, even as an attempt at justification, what is the logic in saying that this will be justified?
(To be honest, in regards to the disagreement between rabbis and rabbis over whether the law of counting is three or five, it seems to be a practical disagreement that comes out of the form of counting words, which further exacerbates the matter.)
Thank you very much.