Right, it was a good API for its time, especially compared to alternatives, most particularly Java's Streams API at the time.

That said, the number of projects I worked on where this new API would have made things so much easier is staggering. It is a shame we can't just fax this API back to our past selves.

The other big building block this uses is Span<T>/Memory<T> which is recent as in this year. Span<T>'s the sort of huge paradigm shift that likely would never have occurred to early .NET design, but starts to seem obvious in retrospect.