Some of the vegan proteins these days are amazing. I've had homemade vegan lasagna that has blown me away. Also pasta sauce with vegan italian sausage that is nearly indistinguishable from the real thing. So good!
Fish... well.... There's no replacing fish.
Thing is, it doesn't have to be black and white. Eating 1/4 your meals as vegan is better than never. Being pescetarian is better than eating all animal proteins. Or even being "vegan plus bacon". Anything is better than nothing. For the environment, your health, and for animal welfare.
"Pure" vegans who say otherwise should pick their battles better.