From what I understood,the gemara asks how could have R. Yosef asked if sefel is like an ambati,since the halachah follows R. Shimon ben Menassiah,and that would mean that it is impossible to mix water for washing the face on shabbat, but with the new okimta that there is no machloket,it comes out that the halachah is the same both for a kos and an ambati, and then the question doesnt even begin since there is no nafka mina,the halachah will always be the same!
Thanks and Yishar Koach for this beautiful work you are doing!
You are correct. According to the Gemara that says that a Sefel (trough) is not like an Ambati (tub) it is permitted to pour cold water into a Sefel. Also, according to the conclusion, that Rebbi Shimon does not argue with regard to pouring hot water into cold water, it is permitted to add hot into cold even according to Rebbi Shimon just like the Tana Kama permits in such a situation.
Be well, Mordecai