So I am definitely not trying to defend LinkedIn but a lot of arguments you make are basically: other sites or services can do that too. Which isn't a great argument to make since monopoly on these will not lead to more usefulness.

The last one I can give a counterargument. You should care because if you are looking for a new job you can try and find people to talk to, which can help figure out if a job you didn't consider so far might be interesting. Maybe the area you work in is not helped with that. I work in R&D and had students reach out to me via LinkedIn just to ask about what kind of work I do at this company and what does the day to day look like. Now not everyone will be happy to talk and not everyone will give you useful answers but then you just go and message the next person.

Downside of this is that LinkedIn makes it artificially difficult to just message people, either promoting their paid subscription or not allowing you to contact people because they are 3rd rate connections or worse. So that's crap again but if you get enough relevant connections this might be better. You can also get sneaky about it and just email a person on their work account by sending a message to firstname.lastname@companyurl.TLD. This you can also only do if you know who works where.