Honestly, if "on break" is replaced with various time-off activities, maybe with a bit more average time spent not working, that would be fine. Alternatively, adding a way to force dwarves to work that causes bad thoughts would be welcome, so if your mason goes on break when you need some walls built to repel an FB you can force him to do it, with an appropriate happiness penalty. Something else that might be nice is if the amount of time spent "on break" is influenced by dwarf happiness. So, a very unhappy dwarf will take more breaks, while a happy dwarf works more. This could be coupled with a system that perhaps evens out the happiness of dwarves, so they are usually content or happy, or maybe very happy if their personality supports it, while they are only ecstatic when big things happen, like making artifacts or having children (or even playing with children, I know many parents are in 7th Heaven just from playing with their young children). On the other hand, things like eating in a legendary dining room could probably be scaled back, or have a lowered effect over time - the first few times they eat there, it's really cool, but then it becomes mundane. This would also encourage changing and adding to older meeting halls, if eventually the dwarves would barely go from content to happy by being there.