There is something wrong in your reasoning in this case. While French does have an intimate relationship with this kind of pronouns that English doesn't quite have, they don't have to be everywhere. Object pronouns replace the objects, so if you don't want to explicit the object, the pronoun in unnecessary. Let's take a look at your examples.
You understand what? Who knows, you just understand in general, most likely what has been explained to you.
Je le comprends.
You understand what? Le. In usual instances, there would be context making explicit what le stands for. Say for example the teacher. You understand him, understand when he's talking. As you can see, it carries a different meaning.
It would be the same thing for the other examples you gave. If you want to define the object that you see, for example, you'll need the pronoun. But in the case of general understanding statements, you actually shouldn't use it. Je vois, je comprends are perfectly correct and used phrases, and are built the same way as in English.
As for j'y viens, it has a different connotation than defining where you're going. It gives off an abstract notion that you are getting to a point. In the cases you want to use the pronoun y, the verb aller will be a better friend.
Tu viens au spectacle ce soir?
Oui, j'y vais.