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 should have clarified by "Landlords" and "Middlemen" I meant the groups that lobby local governments to restrict zoning and growth, so they can retrieve higher profits.
Uber is very much within the "virtuous cycle" – but they may also become rent seekers via monopolization of private transportation.
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.