@twinklecake
I wonder whether he is truly useless or not like you say.
You have seen that he tries to help and even Mary tries to keep him from doing things, she doesn't even let him hold a knife or go into the kitchen, he does try.
I guess he could try to look for a way to learn the language, alas, no one has tried to show him.
He is not pathetic, you are simply used to those isekai protagonist that magically learn the language and gain cheat abilities that help him do that or so I assume, I may be wrong about that.
I don't see anything wrong with him right now, Mary doesn't have a problem with him and she doesn't want him to do things, she also summoned him there and it probably wasn't to make him a butler, there is something going on behind the scenes I believe.
This is something weird to be nitpicky about, a main character that is just laying around in the world he was summoned into.
I would understand if he knew the language and they requested something in exchange for him staying and then refusing to do so while staying.
We all know that if he were asked to do chores, he would do them gladly, especially for Mary.
We know he isn't a bad person, let us not be unnecessarily hard on him or am I missing something crucial that makes him unlikable?
He is in the gray zone for me right now.
You can bet he isn't useless to Mary at least though, she summoned him for a reason, whether that reason is to be a pet or something else entirely is something we will have to see.
Plot twist: He is the demon Lord XD