Nitpicker,
Well, be a nitpicker if you want. I certainly pity you.
Who are the 3 rishonim? Most rishonim hold like the Mechaber. That is the truth. The Rivan’s shita is at variance with R”T, Rambam, Rashba, etc. The Sefer haTeruma holds like neither- he says agrees that if the fish were served or cooked in a meat utensil that they may be eaten with milk. If they were FRIED, however, in a meat pot, they may not. The Sefer Ha-Teruma considers taste transferred directly to the fish as a primary taste. Only when the taste must pass through the medium of water, i.e., bishul, is the taste considered to be “nat bar nat,” a secondary ta’am.
And the Rema says that b’dieved, we can be lenient anyways.