Nintendo is typically a family console/family centered company.
They want to make games that you can enjoy with your family.
You are supposed to cooperate with each other to design the island. It doesnt matter who progresses quicker, gets more resources, etc. Its a group effort. You can have designated areas where one person has the primary control, theres nmt islands for extra resources, you can leave gifts and help each other out whenever.... I dont see why there would be many arguments if any.
If you are arguing over this you should probably save up for a new switch or re evaluate your play style... cant play a multiplayer game thinking its single player. Compromise is important.
That's why we have world of warcraft that we play together. That is why we have sims 4 that we play together. We got the switch and animal crossing for when we are together but doing different stuff. If she is watching her shows I can play the switch. If I'm playing the playstation she can play the switch. When we are out and I am driving, she can play the switch. When we are in the store and i need to tune out because of autism i play the switch. This us why we want 2 different islands. This is not a game or activity we share. This is our time killer app. We pay for a family online plan. We should be able to have our own islands to kill time on.