Clearly their business-as-a-sports-team mentality paid off in spades. But now that spinning up a competing streaming site is "dead simple" (as you put it), they have to compete on content alone, and they're kind of getting their lunch eaten.
I do wonder if their sports mentality starts to break down when it comes to more artistic undertakings. Greenlighting the right projects means bringing the right people together takes a lot of experience and intuition to get right. I think they still have a lot to learn from HBO in terms of focus - it seems like Netflix is still throwing everything at the wall to see what sticks, and to constantly show their customers new movie posters, but for the past few years scrolling through their offerings feels like walking through the unorganized aisles of a giant discount store, when they probably want it to feel like walking into an upscale boutique.
They optimized for a local maxima that's now rapidly eroding, and I think they could theoretically push themselves beyond it, but it seems more likely they'll just throw ads on the thing, or start squeezing and penalizing their users for using the product wrong like the Blockbuster of yore.
More specifically, they have to compete with all of their prior suppliers, who gave streaming rights away for a song, but after Netflix proved the business model, are now charging two arms and a leg for it.
Blockbuster was never a monopoly. Hollywood Video had a comparable number of locations, and there were many smaller competitors. The business model had no real moat.
The details are important, and running a good CDN isn't easy but....it's a CDN serving files. People really did build a completely free version on their own time [1]. That also costs less to run (kind of a requirement if you're building a BitTorrent streaming client).
It's important to think really carefully about what Netflix actually does, as opposed to what they like to pretend they do: because all the important stuff isn't really tech, it's business, bureaucracy and manual labor - subtitling, license management, ISP negotiations for server placement, someone going through every episode of a show to set the "skip credits" titling.
Streaming sites are “good enough” now and will live:die on content.
I honestly have no idea what all that engineering talent is doing such that HBO Max is able to replicate 95% of the technology experience.