Native heterogeneous lists will often be convenient, and sometimes when you've used them they're going to turn out in retrospect to have been a bad idea but sometimes they'll be just fine, especially if they stay fairly locally scoped. I haven't done any serious work in a language that supports them for years, so I don't have a strong opinion about how often each of those cases happens.
But if you decide you want heterogeneous lists, but your language doesn't support them, so you try to implement that with a sum type, then that's basically always going to be a massive pain.
Native heterogeneous lists will often be convenient, and sometimes when you've used them they're going to turn out in retrospect to have been a bad idea but sometimes they'll be just fine, especially if they stay fairly locally scoped. I haven't done any serious work in a language that supports them for years, so I don't have a strong opinion about how often each of those cases happens.
But if you decide you want heterogeneous lists, but your language doesn't support them, so you try to implement that with a sum type, then that's basically always going to be a massive pain.