Being next of kin has no legal standing and you are not legally entitled to make health/care or finance and property decisions on behalf of your relative, which also includes a spouse and prevents the court of protection from stepping in. If the court of protection step in, it’s protracted and expensive and they will make the decisions on behalf of your relative.
A LPA makes sure your wishes are documented and followed, avoids family disputes and prevents court intervention.
Third party access only allows limited access such as paying bills, withdrawing cash, or a debit card for shopping. LPA gives you a much broader authority.
We had a friend whose wife became mentally incapacitated virtually overnight and the court of protection stepped in. He was extremely limited in the decisions he could make for his wife despite being married for 50 years. The process was protracted and costly and I am not sure he ever got over loosing control of being able to make decisions on her behalf.
As part of an LPA you are supposed to discuss your needs and wants with your attorney(s) which should allow them to be able to make decisions in an emergency situation.
In some ways it’s not unlike people not making wills as they think the right things will happen after they die, but having a will makes life so much easier with the estate being quicker to settle. And assuming it has been drawn up correctly, there is no dispute about who the beneficiaries are and what you want them to have.