1- rashi is soiser himself from sotah to other places. the ritva is kneged a velt of rishonim who say techeiles is domeh larakia. the kli yakar and chacham tzvi are acharonim. and when you count acharonim then there is no end to those that say it is blue.
you said “So they obviously didn’t feel that it’s muchach not so from the Gemara” yup and all those who say it is blue also obviously didn’t feel that it’s muchach not so
2- if all the domehs are exact than ain hachi nami domeh lAyam is also davka, and keyadua yam could be this light blue. the rishonim obviously do not go like this chacham tzvi (but the musag that domeh could be lav davka still exists just here is different because the gemara is not mashma like that)
3- I don’t get the point of focusing only on talmudic literature. It is one thing if you are presenting some new metzious the rishonim didn’t know of, but all you are doing is saying the stama is mashma it is green. But if you coming just from pshat who cares? We follow rishonim when it comes to pshat. Besides there are numerous rayos that can’t be ignored that are mevuar it isn’t blue. for example the historians who saw techeiles, or kla ilan and the zohar hakadosh. As for pshat in the yerushalmi, that is the rishonim’s problem.