The space we rented from in Chicago had an open-office first floor and then several stories of small private offices --- where the majority of the tenants worked. Everyone I've ever conf-called with who was in a WeWork, including our NY team, when they were in a WeWork in NY, was also in private offices†, or the WeWork phone booths, which are also better than what most private-office startups have.
I don't know what WeWork you're seeing, but the startup employee experience in WeWorks is generally better, from a professionalism and productivity perspective, than typical startup offices --- if only because they've found a way to scale up cost-effective small private offices.
We ultimately moved to a fairly large private office in Chicago (Chicago commercial space is cheap), and I like it more than I like WeWork, and I don't like WeWork the company at all. But the notion that WeWork isn't providing professional office space is just false; the space they provide is, by a wide margin, more professional than tech industry norms provide.
Unless WeWork outside of NY and Chicago is starkly different than WeWork everywhere else, I don't see how this is even a viable argument. I'm eager to see the counterexample you'll provide.
† (I'm not talking about the WeWork conference rooms, which are excellent and highly professional, so much so that people I knew in Chicago would borrow our WeWork conference credits to hold client meetings in even though they had their own non-WW offices)