You really need to examine the source of every review you read. The internet is full of poorly written reviews from people who have either spent 5mins with an item or worse, haven't used the item at all. There are also plenty of reviews out there that are published by people who "do product reviews" and having something to gain from it, whether it be monetary or social media exposure. For example, I watched a review on YouTube for the 50L done by a guy who also reviewed the Playstation 4, an Accu-rite Weather Station, some ugly and very expensive watch, a Toyota Rav4, and a Gilmore lawn sprinkler. The reviews were all about 5min long...5min for a sprinkler and 5 min for an SUV doesn't convey quality to me. Obviously, he can't be an expert on all of those products. I'm not suggesting a review is worthless if it isn't from a so-called expert, but I put more value if the person has some verifiable experience with the item.
Now onto the 35 Art; your use of the word "durable" seems like you're suggesting the AF mechanism becomes worse over time, or works well and then fails. I have not read anything consistent with that idea and I have not experienced that phenomenon myself. What does seem to be an issue is inconsistent AF accuracy at varying distances. In other words, some people are getting accurate AF with a 6-10ft target distance (just using those values as an example) and inaccurate results with targets outside of that range. I've also heard some say that results are inconsistent at any distance, but for the most part, the negative reviews cite the former example.