in the first line of the first gemara the gaemara starts with a question why dosent it say keitzad ein ha edim neasim zomemim and i cant understand the question because the first tosfot says on the yesh lomar that it is not an edut you cant lehazimam because the hazama is malkut (even though they did not intended malkut for him ela make him ben gerusha or ben halutza)so when the gemara asks why didnt you start with a case that is actually of edim zomemim i could only say that wait THAT IS A CASE . i was thinking maybe the answer is that the question is why dosent the mishna start with a super good case of hazama and not a mediocre case like it did (i also dont like the word mediocre but because of language problems i cant find another word)
Abraham Yohros, panama city, panama
Your answer is the best answer I can think of, with the only drawback being that it does not fit to well in the language of the Gemara (not the end of the world).
I'd like to suggest a similar answer, which is also possibly your intention. "k'Asher Zamam" can be interpreted in a specific way and a general way. The specific way is like you are translating it, meaning that he should have done to him the exact punishment that he planned to do to his friend.
However, it can also be interpreted as meaning that the witnesses should be punished just as they planned to punish their friend, with the emphasis on punishment, not the exact punishment. Chazal determined that this means that the witnesses should be given the exact punishment they planned, unless the Torah says otherwise (as in our cases), in which case the Zomimim get a different punishment.
Accordingly, both the Gemara and Tosfos are correct. The witnesses are still considered to get punished "k'Asher Zamam," as they are being punished like they planned to punish their friend. However, the Gemara is also correct when it says that they are not made into Zomimim, as this case is not a case where the normal intent of the Torah as deteremined by Chazal is fulfilled, since the exact punishment is not given. This is why the Gemara says that the Mishna should say how are they not made Zomimim.
All the best,
Yaakov Montrose