Plenty of electronics have been able to get IP ratings while still having headphone jacks. It’s a trivial part to include as it is practically an ancient bit of tech and doesn’t introduce some kind of massive complexity to the device. Repair is a simple swap of the module. Nothing you’re saying has anything to do with supporting your claim of its removal leading to greater sustainability or reliability. Its materials are no different from the rest of the phone, meaning it’s just as sustainable as the rest of the parts, and it’s not a part that’s prone to failure, meaning it’s just as reliable as the rest.
The Fairphone 5 is less about what comes in the box and more about what you get over the years (www.theverge.com)