I think you could argue the tab names in iOS are way too small and font weight too light to be “good UX”. I worked as a UX designer and consultant… and I dislike rules. The truth always lies somewhere in the grey area.
So “Mystery meat navigation is bad!” is an easy rule to stand behind, however you probably use more mystery meat navigation on a daily basis than you realise. If an app is very simple, with an almost singular purpose e.g. Camera/Instagram, then as long as the icons are recognisable you’re fine to proceed.
Well… proceed into testing. There’s nothing wrong with testing an aesthetically pleasing design when it breaks rules. If your users figure the app out, have no frustration… it can go live. Once live, you can A/B test having labels and see if there’s a significant difference.
The best way for people who are arguing for the aesthetic to drop their argument is to watch user after user to struggle with their design.
The best way to create great designs is to ignore the rules and create something that works for people, something that delights them … and you can’t do that while following all the existing thinking/rules.