Florida does allow separation of Guardianship of the estate and guardianship of the person.
I think we do not want to change the law such that a husband or wife will not be the presumed guardian. Not everyone has a perfect inlaws.
IF there is disagreement, and the parties do go to the courts, then an attorney ad litem should be randomly assigned as the exclusive advocate of the alleged incapacitated person. SOME counties do this as a matter of course. The assigments are random and off a list. I am only aware of one case were the person was actually selected and that was a true emergency and the selection was based on the fact the attorney was known to be physically close at hand. (and the parties were actually in agreement but needed a court finding of incapacity)
must of what you suggest should be done is in fact already the law in the state of FL.
It maybe part of the law, but is not routinely practiced. Go to "Justice for Florida's Seniors."