I'm either not understanding what you are saying or it just doesn't make any sense. It almost sounds like you just want to be able to pay the merits for the other people. That means if you wanted to do an elvaan and paid for it all, you would need 90 merits. You can only hold 45 merits at a time so you would have to get 45 merits, get the items, then have those items waste your inventory space while you get the rest of the merits. After that you have to hold onto all the items while you gather people together, and if you lose or the item you are after doesn't drop your still down 90 merits. Even worst is the other scenario where everyone wants to do mithra but you. Five people want to go, so which of the five is going to have to sponsor you? What's stopping them from just getting a sixth who will pay for themselves?
Could you imagine how less popular delve and incursion would be if everyone needed to get a KI every time for people to enter? Sure right now the price of rocks are low, but if the demand increased 6 fold the prices would shoot up with it. And so what if people spam merit fights. Everyone pretty much already have the chapters they need. The only thing of value that would change is the synthesis material, and they aren't even worth that much on my server already. If anything it would be good if those prices went down, then more people could skill up their crafting.