I haven't seen any of the movies past GoF, but from my experiences in the book fandom, I don't think this is an uncommon opinion. Actually, while I'm sure there are Lupin/Tonks fans, I don't think I know any.

To be fair, a lot of the annoyance I saw was from gay and lesbian fans who liked the idea of one or both of the characters as possibly being gay. And I liked the idea of Tonks being a lesbian, myself, even though I didn't see it supported much in canon. But while I would have been open to the idea of Lupin/Tonks in general, the way the romance was handled in the books did feel like it really came out of nowhere, and in a way that stripped Tonks of the fun personality that made her interesting.

Again, haven't seen the last few movies, but I'd be surprised if the relationship was more developed than in the books.