IMO not having official carrier support is not worth any amount of fairness.
Apple keeps a list of supported carrier features on this page: https://support.apple.com/en-us/HT204039
This used to be more of a problem ~5-7 years ago or so. I'd buy an obscure Android phone and I couldn't use things like Visual Voicemail, Voice over LTE, or WiFi Calling.
Verizon used to be and may still be picky about which phones they activate as well. My Nexus 5X supported all the bands required to work with Verizon, but they refused to activate the phone on their network, despite ordering a plain SIM card for BYOD.
Do you have one, and if so does it feel reasonably snappy?
You really have to be sure that you want a Fairphone for their ethics. Display and camera are particularly very much not great. My past Nexus 5X made much better photos (not sure how much it's just Google's camera app processing at play).
And also if you're not in the EU I would definitely avoid getting one as there's gonna be a lot of hassle with warranty shipments.