I don’t remember if I mentioned this earlier, but regarding the concept of “A mitzvah that could be done by others”, I always assumed that it wouldn’t necessarily apply to a Mitzvah regarding which your doing it is different than someone else’s doing it.
For example, maybe someone could spend time with your kids, but that’s not the same as their father spending time with them. Or someone else can speak to your best friend when he is depressed, but that wouldn’t be the same as your speaking to him.