But what differentiates them from any other company that rents out commercial real estate and re-leases it on a shorter term?

I can totally believe that their line of business will grow by a huge factor, but I don't believe that they will ever earn the out-sized margins to justify their current valuation. Their business can be replicated by anyone with a bit of capital to spend on leasing office space. They don't actually own most of their office space; they just lease it.