Thanks for the chapter!
Comment in displayed comment page 16 should say Descended not Ascended to the Ground Realm too. She even said descended in page 8. After all, in most cultures and manga/LN the gods in charge of running things are usually in the heavens above the world. Whether that means really high up in the sky, in orbit, or where they have the window/door to look at things or insert things into the world from another dimension/hammerspace is unknown. That and deep underground is usually where evil beings live or imprisoned such as the spirits of evil people as if to show the world itself is judging and imprisoning them.
As for the goddess, as MC said if they weren't sealed they wouldn't need heroes and could unintentionally affect the world with just their presence. Similar to how Soul Society lieutenants and captains along with the badge given to MC suppress their powers to avoid affecting the living in "Bleach." After all, if she used a spell to kill a goblin or swung a blow that ended up destroying half the continent that would really be bad. In any case, I doubt she's useless, just need to know what she can and can't do while sealed and she provides the MC someone to talk to while traveling. It's not like the goblins would be great conversationalists with their limited vocabulary assuming that the MC's language skill can even translate what they say to him. Besides, I get a sense of foreshadowing when she mentioned that she's unsealed within the ball. Which means that within the ball she's unfettered and can use everything. So if can cast or do something while in the ball to affect outside the ball it could be really useful. That and if can get a strong enemy can't defeat in the ball she can whallop it inside the ball. Or from a practical standpoint she could use her powers to make high quality blessed objects or equipment to sell albeit would need to be careful about that as flooding the market with high tiered blessed stuff would wreck the economy and attract trouble, such as merchants or government officials wanting to steal/control such things for personal gain. After all, with goddess tier equipment that are a dime a dozen who's going to want to buy lower grade stuff from the local blacksmiths or from monster drops?