Rice in the instant pot is fine, but it’s a bit more hands on. The rice cooker makes it perfect automatically every time after you put the ingredient in and just press a button. You can also keep the rice warm the entire day so you can make some for breakfast and just use it throughout the day, hot and ready to eat! The convenience of not needing to babysit the rice, put leftovers away right after making it, no chance of burning the rice, every individual grain cooked perfectly etc. It’s worth it. When you have equipment that makes something, normally mediocre, exceptional every time you end up eating it way more often.
Edit: I realize the instant pot has a keep warm function too, but I often make something in my instant pot to go with the rice so it’s better to have a rice cooker for that reason as well.