By the monopoly phone provider's logic, it did "get better" after it was reclassified.

(This is where AT&T switched to "Uverse" fiber-to-the-neighborhood network, with speeds up to 40+mbps. And since that's an "information service", no other companies are allowed to use it to sell internet, even though it's literally the same phone line as DSL, with almost identical technology and performance seen in other countries faster DSL services)

I guess I'm a little confused. The last mile unbundling would have just been the node-to-home lines, would it not? A new ISP entering the market would be able to lease those, but not necessarily the fiber network? Or would that fiber network have been unbundled too?

That is mostly a technology issue. There is a maximum bitrate at which the transmission line can support for a given distance. To get past that, they have to start dragging fiberoptics to nodes they build closer to your house. Before you hit that speeds, protocol upgrades were giving you faster speed.

And I wouldn't say "very select regions." At least a quarter of the country live in areas with FTTN or FTTP networks deployed by the telecoms.