I think tortles 17 AC is worthwhile, provided their shells can be enchanted. For everything else it should be at least 13+ dex to match mage armor and be an actual benefit over studded leather.
While I know it would never happen, I do wish it followed the PF2E model a bit more, and added proficiency to AC. Rather than everyone getting the exact same proficiency bonus once proficient, it allows for granularity with trained (+2), expert (+4) master (+6) and legendary (+8). Monks start with expert unarmored defense, so add 4 to their AC. They also have a stance for strong monks that doesn't allow Dex to AC but gives a large AC buff, letting you make something like a sumo or other big beefy tough guy. Would be nice to have stronk monks!