This is a blog post spoiler. When you weigh the pros and cons of universal family trees against those of private family trees, the universal tree always wins. By no means, am I undertaking to compare individual programs, the issues I see of overriding importance duplication of effort and preservation. As I have written many times previously, if you privatize your genealogical research you are almost certainly insuring its loss. I have never been able to understand how ownership became an issue with genealogical research. The reason why I come back to this topic from time to time is usually based on someone telling me why they can't share their research or their pedigree or whatever. See https://genealogysstar.blogspot.com/2022/01/you-cant-take-it-with-you.html
Here is the list of reasons why a universal family tree, despite their inherent failings will always be a better idea that a closed, private family tree. I'll start off with private family trees.
Pros of a private family tree
1. The person who "owns" the private family tree is totally responsible and answerable for its content.
2. All changes are predictable because only one person (or a very small number of people) can make any changes.
3. The owner of the private tree does not have to answer to anyone about the content or accuracy of the incorporated information.
Cons of a private family tree
1. There is a very high probability that when the owner dies, the information contained in the family tree will be lost.
2. If the private family tree is not lost, it is also probable that anyone who inherits the information will consider it to be the Truth about the family and any errors will be perpetuated for many more generations.
3. Because a private family tree is not, by design, cooperative, it is also possible that the information found and incorporated by the owner is incomplete and may also be inaccurate. I make this comment because of the many times my own entries in public family trees have been corrected or added to.
Pros of a universal, cooperative, source-supported family tree
1. Duplication of effort is minimized with all the information available to all users.
2. Open wiki-based websites have a tendency to become more accurate over time because any information entered can be verified or changed by any user.
3. A cooperative family tree can ultimately contain more information than any privately maintained family tree.
4. Depending on the sponsor, information is preserved even when a user dies.
Cons of a universal, cooperative, source-supported family tree
1. Users' frustration level is high because of claims to ownership of genealogical information.
2. Specific changes can be arbitrary and inaccurate because of differing levels of expertise.
3. Resolution of real historical controversies is difficult because of the universal nature of the venue.
The solution to deciding between a private and a public universal family tree is mainly resolved by individuals using both venues. If a genealogist wishes to make their information private, they should take steps to prevent loss of their work after death.
By the way, dead people very limited post-mortem privacy. See Post-mortem privacy for a start.
Despite any perceived or real shortcomings of universal, cooperative, source-supported family trees, I am strong advocate for their use, including the FamilySearch.org Family Tree, WikiTree.com, and Geni.com.