Sure it is a relevant book, especially in leftist history work. The problem scholars have with it is that it is held up as the text by some laypeople. It is not unique in having narrative issues. That's true of all history. It is just frustrating to see people say "well, he didn't get any facts wrong so all criticism is invalid".
No, I would never say all criticism is invalid. I think it's a relevant and important text to read, along with criticism of it. Nothing should be taken in isolation, scholarship is ultimately a conversation at a high level between knowledgeable parties, and it's a pretty dated book in a lot of ways. Nonetheless it was extremely influential and solid as a basic leftist history text, and he even acknowledges its bias in the preface and title as I've mentioned. I don't by half think it's a perfect book and I have a lot of criticisms of Zinn.