They can generate good responses for things that are low stakes and require no new thinking. Fitness and nutrition are fairly established (although I’m sure I could get it to give me bad nutrition advice) so the responses can be pretty accurate for those fields.
I also think you should give a lot of credit to yourself for hitting your goals. For 95% of people, no new information is needed to lose weight or change their diet. People naturally have a good idea of what is good for them and how to lose weight. What is needed is consistency and motivation. It seems like the AI was a great accountability buddy, but you’re still the one who ultimately did the work!