It is, but it provided a ton of web-centric APIs in an era where people published useful RSS feeds. Half the value was in publishing modules that spoke RSS in some form, and the other half was a number of online query systems that spoke HTTP and responded with RSS.
There were many technical problems with pipes and one major business problem. The technical problems as usual, were solvable:
- branching. the system really didn't have a clean way to cause branching. if you wanted to only apply a regex on certain items, that would fail hard. I feel like some part of the anime fansub system I built must have been stressing the system because I'd occasionally find it disabled or key components removed from Pipes. (Deluge can consume RSS in the background, but often the fansub RSS feeds have duplicate items for different qualities, or are missing the enclosure field the system keys off of and other field normalization problems)
- types. the system really operated on RSS as a medium of data exchange. Any operation that worked on whole RSS feeds was great. So the typical 'put a ton of blogs into a pipe and union them all into one big feed' hello world app worked great. As soon as you wanted to operate on a specific line of input items and do subprocessing, you were in a sort of hell. It wasn't clear which modules worked on which types, or why.
- composition. a general engineering principle is to build things out of small parts. That's the fundamental reason pipes works, but you never had the ability to treat a pipe you built as a small part itself. You couldn't build pipes that accepted RSS in. The subpipe command they eventually added only allowed RSS out, without even any parameterization. Judging by the comments from support engineers here, the reason is mostly obvious: they couldn't prevent people from building pipes that called themselves indirectly.
But the business problem was most fundamental. The most useful APIs were often monetized via web ads. Yea, someone was collecting amazon referral revenue, but beyond that, no money was changing hands. That was a fundamental challenge to further adoption. Bloggers started publishing truncated or headline blog feeds, and what sort of evolved was a cat and mouse game with content creators: people invent new ways to generate RSS feeds for sites that don't have them while the sites fuzz their UI to prevent it.