Nope, not sarcastic. Apple specifically notes that they designed their Watch product to have value to people after they reach their goals, not just during the trek towards the goal. I consider their statements to indicate that they apply the same considerations to "weight targets" – gain/loss, followed by maintenance – as they would to any other health target, such as those they measure with Activity rings today.

https://www.theverge.com/2018/1/24/16926350/apple-watch-seri...

“The idea that small behavior changes can actually add up to something great is a real core philosophy of the activity app,” says Blahnik [director of fitness and health at Apple]. “Partially because what we find is that’s going to correct everybody. If you’re a beginner, and you’re not very fit, small changes are what you need to do. But it turns out that if you’re really fit, small changes are all you have left. So, it ends up being something that actually works for everybody.”