I know you're not OP and I understand this is the definition of rent-seeking behavior, but your examples are empirically and theoretically invalid. Landlords (renters of capital) and middlemen provide huge benefits to society.

Of course, this doesn't mean that it's impossible for a landlord it middleman to be a rent-seeker, but they would need to pursue some type of artificial benefit/restriction on others in order for this to be the case. This does happen often, but I have no idea why OP would suggest rent-seeking is the primary activity of sharing economy companies. One of Uber's greatest accomplishments has been significantly weakening the rent-seeking taxi industry.

I think we'd agree that a large portion of the current world economy is driven by rent seeking.

Yes, but how does that apply to the sharing economy? Uber has added immense value to my life and the lives of it's millions of satisfied customers.